JPH04145926A - Exhaust gas purifying material and purifying method - Google Patents

Abstract

PURPOSE:To effectively remove both of particulate carbon matter and NOx in exhaust gas by using a purifying material obtd. by depositing a catalyst comprising an alkali metal and a specified transition metal and a rare earth metal on a porous ceramic layer provided on a heat-resistant porous filter. CONSTITUTION:A purifying material used is prepared by depositing a catalyst comprising an alkali metal and a specified transition metal and a rare earth metal on a porous ceramic layer provided on a heat-resistant porous filter. The material to form the filter is a ceramics such as alumina, silica, zirconia, etc. The alkali metal is preferably lithium, sodium, potassium, and cesium. The specified transition metal is Cu and V. The rare earth metal is cerium, lanthanum, neodymium, etc. With this filter, particulate carbon matter in exhaust gas from a diesel engine or the like is oxidized, and simultaneously, these particulate carbon matter acts as a reducing agent to reduce NOx.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an exhaust gas purification material and an exhaust gas purification method using this exhaust gas purification material. (hereinafter referred to as particulates) and particulate carbon materials (hereinafter referred to as particulates)
The present invention relates to an exhaust gas purification material that can simultaneously remove the following: and an exhaust gas purification method using the exhaust gas purification material.

[Problems to be solved by conventional techniques and inventions] In recent years,
Particulate carbon substances (mainly composed of solid carbon particles, called particulates), NOx, etc. in exhaust gas emitted from diesel engines and the like have become a problem as harmful to environmental health. In particular, particulates have an average particle size of 0.1 to 1 μm, and are easily absorbed into the human body through airborne air or breathing, and recent clinical test results indicate that they also contain carcinogenic substances. This has been confirmed.

As methods for removing particulates, the following two methods are being considered depending on the person. The method is to trap particulates by filtering the exhaust gas using a heat-resistant filter, and when the resulting pressure loss increases, the filter is regenerated by burning the trapped particulates with a burner, electric heater, etc. It is. Heat-resistant filters that can be used include honeycomb ceramic filters, foam ceramic filters with a three-dimensional mesh structure, steel wool, wire mesh, and the like.

The other method is to filter particulates and self-combust them using the action of a catalyst supported on a filter as described above.

In the former case, the higher the particulate removal effect, the faster the pressure drop will rise, and the more frequently the regeneration will occur.
High reliability is required for reproduction, and it is considered to be economically disadvantageous.

On the other hand, the latter method is considered to be a much better method if there is a catalyst that can maintain catalytic activity under the exhaust gas emission conditions (gas composition and temperature) of a diesel engine.

However, since diesel engines use light oil as fuel, the exhaust gas contains a large amount of 802, and the oxygen concentration in the exhaust gas varies over a wide range of 2 to 20% depending on the operating conditions of the diesel engine. Under such exhaust gas conditions, a method for regenerating an exhaust gas purification filter that satisfactorily ignites and burns the accumulated particulates and does not cause secondary pollution has not yet been established.

For example, the catalysts proposed so far for purifying particulates in exhaust gas from diesel engines, etc.
There are noble metal-based and base metal-based catalysts, but noble metal catalysts have low durability, CD, and unburned hydrocarbons (hereinafter referred to as l).
Although it has high oxidizing properties such as (referred to as c), it easily converts S02 present in exhaust gas into 803, and is highly likely to cause secondary pollution. It also has the disadvantage that the soot in the particulates deteriorates the combustion characteristics. On the other hand, base metal catalysts are effective as particulate purification catalysts, but have problems in terms of durability.

In addition, most of the exhaust gas purification catalysts and purification materials proposed so far have focused on lowering the ignition temperature of particulates, and the oxygen concentration in the exhaust gas is generally high or changes significantly. Removal of NOx contained in exhaust gas from diesel engines and the like remains unresolved.

Therefore, an object of the present invention is to provide an exhaust gas purifying material that can efficiently burn and remove particulates contained in exhaust gas with large changes in oxygen concentration, such as those emitted by diesel engines, and at the same time, can also effectively remove nitrogen oxides. An object of the present invention is to provide a method for purifying exhaust gas.

[Means to solve the problem]

As a result of intensive research in view of the above issues, the present inventor has discovered that an alkali metal element, a specific transition metal element, and a rare earth metal element are added to a porous ceramic layer provided on a heat-resistant porous filter. We discovered that by using a purifying material that supports a catalyst, it is possible to efficiently remove particulates and NOX at the same time even in exhaust gas where the oxygen concentration changes greatly, and that the removal ability lasts for a long time. The invention has been completed.

In other words, the exhaust gas purifying material of the present invention comprises (a) an alkali metal element, (b) a Cu element and a V element, and (c) a rare earth element on a porous ceramic layer provided on a heat-resistant porous filter. It is characterized by supporting a catalyst.

Further, the exhaust gas purification method of the present invention is characterized in that, using the exhaust gas purification material, particulates in the exhaust gas are oxidized by the catalyst supported on a filter, and at the same time, nitrogen oxides are reduced using the particulates as a reducing agent. do.

The present invention will be explained in detail below.

Since the filter of the present invention filters high-temperature exhaust gas, a material that is porous and has high heat resistance, particularly high thermal shock resistance, is used as the material for forming the filter. Moreover, it is necessary that the pressure loss be within an allowable range while maintaining the necessary particulate collection performance. Such filter forming materials include alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia,
Examples include ceramics such as alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, and cordierite.

The porosity of the filter is preferably 40-80%.

The shape and size of the filter can be varied depending on the purpose, but it is generally cylindrical, with a diameter of 30 to 400 mm and a thickness of 50 to 300 mm. Moreover, if necessary, a plurality of sheets may be laminated.

The catalysts supported on the above filter include (a) alkali metals (Li, Na, K, Cs, etc.) and (b)
) Cu and V, and (c) rare earth elements (ce SLa,
(Nd, Sm, etc.) is used.

By using the catalyst configured as described above, particulates in exhaust gas can be ignited and burned at a relatively low temperature, and NOx can be effectively removed. That is, the particulates in the exhaust gas coexist with the catalyst element and oxygen in the filter, thereby lowering the ignition temperature and burning (oxidizing) the particulates at 400° C. or lower. At the same time, the particulates act as a reducing agent to reduce NOx, thereby effectively purifying the exhaust gas. In this way, N at relatively low temperatures.

The reason why the reduction of x occurs efficiently is thought to be due to the synergistic effect caused by the simultaneous presence of the particulates in the exhaust gas and the above catalyst components (a), (b) and (c).

For simultaneous removal of NOX and particulates, a catalyst consisting of an alkali metal, a transition metal, and a rare earth metal, especially Cu as the transition metal, has excellent purification ability in the initial stage of use. If the above three elements (alkali metal, Cu as a transition metal, and rare earth metal) are simply combined, the purification properties of the catalyst will gradually deteriorate due to the presence of sulfur and its oxides contained in the exhaust gas.

In particular, since the exhaust gas is at a high temperature, sulfur oxides such as S[12] rapidly deteriorate the purification properties of the catalyst.

Therefore, in the present invention, as (b) transition metal, C
Use u and V. By adding (ii), that is, a combination of alkali metals, Cu, and v1 rare earth metals, it is not expected that the initial properties of the catalyst will be significantly improved, but stable simultaneous removal properties of NOx and particulates can be obtained over a long period of time. .

(a) Alkali metals include lithium, sodium,
Preferably, potassium and cesium are used. (3) Cu and V are used as transition metals. Furthermore, as the rare earth metal (c), it is preferable to use cerium, lanthanum, neodymium, or the like.

The amounts of each of the above catalyst components (a), ra) and (c) are as follows:
The weight ratio of each metal component is 10 to 50% (a),
(a) is preferably 30 to 90%, and (c) is preferably 10 to 50%. In addition, the ratio of Cu and V in (ra) is 5/1 by weight
It is best to set it to about 1/15.

To support the above-mentioned catalyst on the heat-resistant porous filter, a carrier layer made of ceramic, which is more porous and has a larger surface area than the filter, is formed on the filter, and then the catalyst is supported on this carrier layer.

Materials for forming the carrier layer include titania, alumina,
Using porous and large surface area ceramics such as silica, titania-alumina, titania-silica, etc., the amount supported is
In the case of a ceramic filter, the amount is 3 to 15% by weight, preferably 5 to 12% by weight of the filter. The total amount of catalytically active species is 1 to 40% by weight, preferably 5 to 30% by weight of the carrier.

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

The wash coat method is a method in which a carrier layer is formed on the filter by immersing the filter in the above-mentioned porous ceramic slurry and drying it.

Further, the formation of the carrier layer by the sol-gel method is performed as follows.

The organic salt of the metal (e.g. alkoxide) that forms the ceramic for the carrier layer is hydrolyzed, the resulting sol is coated on a filter, a film of colloidal particles is generated by contact with water vapor, etc., and then dried and fired. to form a catalyst carrier layer on the filter. For example, when using titania (T102) as the ceramic for the carrier layer, first a Ti alkoxide (e.g., Ti(0-iso C3H7)
4) Into the alcohol solution, Cll3COOH, HNO3
, to produce a coating liquid to which an acid such as HCβ is added. After immersing the filter in this coating liquid and pulling it out,
Gelation is achieved by reacting with steam or water. Then,
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 during gelation, but the hydrolysis reaction can also be promoted by adding an alkali instead of the acid.

Although titania has been described above as an example of the ceramic for the carrier layer, other ceramics can be similarly supported by the sol-gel method. For example, when forming an alumina carrier layer, an octaβ alkoxide is used and the same method as in the case of titania described above is used. The same applies when using other porous carriers.

By the above-mentioned wash coat method or sol-gel method, etc.
After forming a porous ceramic carrier layer on the filter, the carrier layer is impregnated with an aqueous solution of catalytically active species such as carbonate, nitrate, acetate, and hydroxide, and then dried and fired again. Supports the catalyst. As the salt of the catalytically active metal species, any salt can be used as long as it dissolves in water, such as carbonates, nitrates, acetates, and hydroxides, as described above. ■ is responsible for NH4
A solution of VO3 and oxalic acid can be used. Furthermore, an alkali metal and V can be simultaneously supported using an alkali vanadate.

〔Example〕

The present invention will be explained in more detail by the following specific examples.

Example 1 Cordierite ceramic foam (apparent volume 2
1. The filter was coated with 10% (weight %, the same applies hereinafter) of TlO2 by the wash coating method.

The obtained filter was impregnated with Cu, La and Cs at 2.5% relative to TiO2 using aqueous solutions of CuCl2, La(NO3)+ and CsNO3, and after drying,
It was fired at 00°C. Next, the filter obtained above was treated with NH and VO.

It was immersed in a mixed aqueous solution of oxalic acid and impregnated with 2.5% of ■. After drying this filter, it was fired again at 700° C. for 3 hours to obtain a purifying material.

For this purifying material, using a diesel engine with a displacement of 510 cc, the temperature at which the particulates ignite and burn and the filter is regenerated (the temperature at which the pressure loss decreases) and the conversion rate of NOx at that time were determined. Ta. In addition,
The regeneration temperature and NOX conversion rate are determined at two points: at the beginning of the use of the purification material (when a decrease in pressure loss is observed for the first time) and at the time when the pressure drop decreases after 10 hours of using the purification material. It was found in The engine is operated at a rotation speed of 15
It was set to 0 rpm and the load was set to 90%. Under these operating conditions, the total amount of HC in the exhaust gas is 90 ppm SC
O is 460 ppm, NOX is 480 ppm, 02
was 10%, and SO2 was 200 ppm.

The results are shown in Table 1.

Examples 2 to 4 In the same manner as in Example 1, 1 TlO2 was added to the foam filter.
0% coated with CuCl2, Ce(NL)3 and C8N
Cu, Ce and Cs were converted to TlO using each aqueous solution of O3.
The two layers were impregnated at 2.5% each, and dried and fired in the same manner as in Example 1. Next, V
A purification material was obtained in which 2.5% of Cu, Cs, Ce and V were supported (Example 2).

Similarly, CuCl2, La(NO3)3, and K
Each aqueous solution of Cl and N11. VD, using an aqueous solution, Cu
, La, K and V to TlO2, respectively.
A purifying material having a loading of 5% was obtained (Example 3).

Furthermore, using CuCl2, Ce(NO3)3, KCl, NIl, VO, and aqueous solutions, a purification material carrying 2.5% each of Cu, Ce, K, and V was obtained (Example 4).

For each of the obtained purification materials, the regeneration temperature and NOx purification rate were determined in the same manner as in Example 1.

The results are shown in Table 1.

Comparative Examples 1 to 4 Using the same cordierite foam filter as in Example 1, 10% TiO2 was supported on the filter by the wash coating method.

For the obtained filter, La (NO3) 3,C
Using uCL, C3NO3, and KCff aqueous solution, a purification material supporting the following metals was created. The method of supporting each metal was the same as in Example 1, and the amount of each metal supported was 2.5%.

Comparative Example 1: Cs/Cu/La Comparative Example 2: Cs/Cu/Ce Comparative Example 3: K/Cu/La Comparative Example 4: K/Cu/Ce The obtained purification material was recycled in the same manner as in Example 1. The temperature and N[]X removal rate were determined.

The results are shown in Table 1.

Table 1 Note (1): The point at which the first decrease in pressure drop is observed.

(2): When the pressure loss decreases 10 hours after gas starts passing through the filter.

(3): NOX in exhaust gas before and after passing through the filter
NOx purification rate (%) calculated from the amount.

As is clear from Table 1, the exhaust gas purification material of this example has a higher NOx purification rate than that of the comparative example even after 10 hours have passed since the start of use. Also, the regeneration temperature of the filter at that time (the temperature at which particulates are ignited and burned) is low.
It can be seen that the exhaust gas was well purified.

〔Effect of the invention〕

As explained above, by using the exhaust gas purifying material of the present invention, both particulates and nitrogen oxides in the exhaust gas can be effectively removed. Further, even relatively low-temperature exhaust gas from a diesel engine or the like can be efficiently purified.

The purifying material of the present invention can first be applied using a wash coat method or a sol method.
A porous ceramic layer is formed on the filter using a gel method, etc., and the catalyst is supported on the ceramic layer.
The catalyst is evenly supported on the filter at a high concentration, resulting in good exhaust gas purification performance.

In addition, the purifying material of the present invention contains Cu as a transition metal in the catalyst.
and V, it is possible to simultaneously remove NOx and particulates satisfactorily over a long period of time without degrading the purification characteristics even in exhaust gas with a high SO2 concentration.

The purifying material of the present invention is Eye Exhaust from gel engines, etc. Suitable for gas purification.

Out wish Man KK formula hand Continued Supplementary Positive Calligraphy (self-published) October 8, 1991 1990 Patent Application No. 270200 name of invention Exhaust gas purification materials and exhaust gas purification methods person who makes corrections Relationship to the case Patent applicant Name Riken Co., Ltd.

Claims (3)

[Claims] (1) An exhaust gas purifying material comprising a catalyst supported on a porous ceramic layer provided on a heat-resistant porous filter, the catalyst comprising (a) an alkali metal element, and (b) a Cu element and a V element. and (c) a rare earth element. (2) The exhaust gas purifying material according to claim 1, wherein the ceramic layer is TiO_2. (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 oxidized by a catalyst supported on the filter, and at the same time, the particulates are oxidized by a reducing agent. An exhaust gas purification method characterized by reducing nitrogen oxides.