JPH04145927A - Exhaust gas purifying material and purifying method - Google Patents

Abstract

PURPOSE:To remove both of particulate carbon matter and NOx in exhaust gas by using a purifying material obtd. by forming a catalyst layer comprising a mixture of ceramic powder carrier and a catalyst comprising an alkali metal and a specified transition metal and a rare earth metal with a specified mixing proportion on a heat-resistant porous filter. CONSTITUTION:A purifying material used is manufactured by forming a catalyst layer comprising a uniform mixture of ceramic powder carrier and a catalyst comprising an alkali metal and a specified transition metal and a rare earth metal on a heat-resistant porous filter. The mixing ratio is to 100 pts.wt. of the filter, 1-20 pts.wt. of catalyst and 1-10 pts.wt. of ceramic powder carrier. The material to form the filter is a ceramics such as alumina, silica, zirconia, etc. The alkali metal is lithium, sodium, potassium, and cesium, prefeably. The specified transition metal is Cu and V. The rare earth metal is cerium, lanthanum, neodymium, praseodymium, etc., preferably.

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. The present invention relates to an exhaust gas purification material that can simultaneously remove particulate matter (hereinafter referred to as "particulates") 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 matter (mainly composed of solid carbon particles, referred to as particulates), NOx, and the like in exhaust gas discharged 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 suspended in the air, so they are easily taken into the human body through breathing, and recent clinical test results show that they also contain carcinogenic substances. This has been confirmed.

The following two methods are being considered as methods for removing particulates. One method is to capture particulates by filtering exhaust gas using a heat-resistant filter, and when the resulting pressure loss increases, the filter is regenerated by burning the captured 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 maintains 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 SO□, 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-based catalysts are more durable and produce CO1 and unburned hydrocarbons (hereinafter referred to as HC).
Although it has high oxidizing properties such as (referred to as ), it is easy to convert SO2 present in exhaust gas into SO3, and there is a high possibility of producing secondary pollution. It also has the disadvantage of reducing the combustion characteristics of the media in the particulates. On the other hand, base metal catalysts are effective as catalysts for purifying particulates, 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 inventors have discovered that a catalyst consisting of an alkali metal, a specific transition metal, and a rare earth metal, and a ceramic powder carrier are uniformly mixed on a heat-resistant porous filter. By using a purifying material that has a catalyst layer formed of a They discovered that it is possible to reduce the size of the device, and completed the present invention.

That is, the exhaust gas purifying material of the present invention has a catalyst comprising (a) an alkali metal element, (b) a Cu element and a V element, and (c) a rare earth element, and a ceramic powder carrier on a heat-resistant porous filter. A catalyst layer made of a homogeneous mixture is provided, and the amount of the catalyst is 1 to 20 parts by weight and the amount of the ceramic powder carrier is 1 to 10 parts by weight per 100 parts by weight of the filter.

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 used in the present invention filters high-temperature exhaust gas, the material from which it is formed 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 necessary particulate collection performance. Examples of such filter forming materials include ceramics such as alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, and cordierite. It will be done.

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, La,
(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 N[]X, and the exhaust gas is effectively purified. In this way, NOx is generated at relatively low temperatures.
The reason why the reduction 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 catalyst segments (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 802 cause a rapid deterioration in the purification properties of the catalyst.

Therefore, in the present invention, as (b) transition metal, C
Use u and V. By adding (2), that is, a combination of alkali metals, Cu and V, and rare earth metals, although it is not expected that the initial characteristics of the catalyst will be significantly improved, stable simultaneous removal characteristics of NOx and particulates can be achieved over a long period of time. It will be done.

(a) Alkali metals include lithium, sodium,
It is preferable to use potassium and cesium, and (c) as the rare earth metal, it is preferable to use cerium, lanthanum, neodymium, praseodymium, etc.

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 weight ratio of Cu and V in (b) is 5/
It is preferable to set it to about 1 to 1/15.

The above-described catalyst is uniformly mixed with ceramic powder serving as a carrier, and then supported on a thermoporous filter. That is, a catalyst layer made of a uniform mixture of the above catalyst and ceramic powder is formed on the heat-resistant porous filter. This catalyst layer can be formed, for example, by a wash coating method, a sol-gel method, etc., which will be described later. According to such a method, the catalyst layer can be made into a porous layer, and the contact area with exhaust gas becomes large.

Ceramic powders used as carriers include titania, alumina, silica, titania-alumina, titania-silica,
Porous ceramics with a large surface area can be used.

The amount of catalyst supported is 1 to 20 per 100 parts by weight of the filter.
Part by weight. 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 an amount of catalyst exceeding the upper limit is supported, the exhaust gas purifying ability 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.

Further, the amount of ceramic powder serving as a carrier for the catalyst is 1 to 10 parts by weight per 100 parts by weight of the filter.

If the amount of ceramic powder is less than the above lower limit, it is not preferable because it will not be able to support a sufficient amount of catalyst. on the other hand,
If the amount of ceramic powder exceeds the above upper limit, the pressure loss in the purifying material will become too large. The preferred amount of ceramic powder is 2 to 6 parts by weight.

Formation of the catalyst carrier layer (porous ceramic layer) by the wash coating method involves impregnating the catalyst in advance with ceramic powder such as titania, and then immersing the filter in a slurry of the ceramic powder containing the catalytically active species. You can do it by doing this.

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

ClCl is added to an alcohol solution of a metal organic salt (for example, when the ceramic layer is made of TiO□, use a Ti alkoxide, etc.) that forms the ceramic layer that becomes the catalyst carrier layer.
A coating solution is prepared by adding an acid such as 3COOH, HNO, .)ICff and an aqueous solution of a salt of a catalytically active metal species. Next, after the filter is immersed in this coating solution, a film of colloidal particles is formed on the filter by contact with water vapor or the like, and then dried and fired to form a porous ceramic layer containing a catalyst on 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.

Note that even when the catalyst carrier layer is formed of ceramics other than titania, the same method can be used. For example, in the case of forming an alumina carrier layer, an alkoxide of A1 may be used. The same applies when using other porous ceramics.

As the salt of the catalytically active metal species, any type of salt can be used as long as it is soluble in water, such as carbonate, nitrate, acetate, hydroxide, etc. For the carrier (2), a solution of NH, VO2 and citric acid can be used. Furthermore, an alkali metal and V can be simultaneously supported using an alkali vanadate (for example, potassium vanadate, sodium vanadate, cesium vanadate, etc.).

As mentioned above, the exhaust gas of the present invention has a catalyst layer on its surface made of a uniform mixture of catalyst and porous ceramic powder, so even if the amount of ceramics serving as a catalyst carrier is small, a relatively large amount of catalyst can be carried. can be supported, thereby reducing the pressure loss of the filter. That is, a large amount of catalyst can be supported on the filter even with a small amount of ceramics that does not cause a large pressure loss.

〔Example〕

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

Example 1.2 A predetermined amount of Ti alkoxide (Ti (0-iso C
3L) Add acetic acid to the alcohol solution of 4),
Predetermined amount of CuC1□, La (NO3) a, CsN
A coating solution was prepared by adding an aqueous solution of O3 and a mixed aqueous solution of Nl, VO3, and citric acid.

Cordierite ceramic form (apparent volume 0
．． 257! , with a density of 0.658/mI, was used and immersed in the above coating solution.

This foam was taken out and steam was applied to it to convert the coating liquid into a sol and then into a gel. After drying,
The product was fired at 600° C. for 3 hours to obtain a foam filter in which a ceramic layer containing a catalyst was formed. The amount of T10□ supported on the filter was 3% (weight%,
The same applies hereafter).

Further, the amounts of Cu, La5Cs and V were 1.5% relative to the filter.

(Ti02: C8/Cu/V/La: Example 1) In the same manner as in Example 1, La (NO3) a
Using Ce(NO3)+ instead of , a filter having the following catalytically active metal species was created.

(Tin2: Cs/['u/V/Ce: Example 2) The amount of TlO2 supported on the filter was 4% with respect to the filter, and CsS[:u, V and C
The amount of e supported on the filter was 1.5%.

A purifying material having an apparent volume of 11 was obtained by stacking four sheets of each of the puirters of Example 1 and Example 2.

For this purification material, a diesel engine with a displacement of 500 cc was used, and the pressure loss caused by capturing particulates, the temperature at which the particulates ignite and burn and the filter is regenerated (the temperature at which the pressure loss decreases), and , the NOX conversion rate at that time was determined. The regeneration temperature and NOx conversion rate are the same at the beginning of the use of the purifying 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 purifying material. It was calculated at two points. When operating the engine, reduce the number of revolutions to 2
It was set to 50 rpm and the load was set to 80%. Under these operating conditions, the total amount of HC in the exhaust gas is 90 ppm of all hydrocarbons, and C
D is 460 ppm, NOX is 480 ppm, 02
was 10%, and SO2 was 200 ppm.

The results are shown in Table 1.

Example 3.4 Potassium titanate, La(NO3)3, and Cu(N
o3) A slurry consisting of a mixed aqueous solution of 2, NH, VO3, and oxalic acid was prepared.

A filter similar to that in Example 1 was immersed in this slurry, taken out, dried, and then fired at 700° C. for 3 hours to obtain a foam filter on which a ceramic layer containing a catalyst was formed.

(T102: K/Cu/V/La: Example 3) The amount of TlO□ for this filter is 3%, K is 3% for the filter, and Cu and La are each 2% for the filter. there were. Further, V was 2%.

A filter having the following catalytically active metal species was prepared in the same manner as in Example 3 using Ce (NO3) 3 instead of La (NO3) 3.

(Tie: K/Cu/V/Ce: Example 4) In this filter, the amount of TlO2 carried is 3% with respect to the filter, and K is 3% with respect to the filter.
%, and Cu and La are each 2% for the filter.
%Met. Further, V was 2%.

The filters obtained above were each used in the same manner as in Example 1.
The layers were stacked to form a purifying material, and the pressure loss was reduced in the same manner as in Example 1.
The temperature and NOX conversion rate at that time were measured. Both results are shown in Table 1.

Comparative Examples 1 to 4 A TlO2 layer containing the catalytically active metal described below was formed on the same cordierite foam filter as in Example 1 in the same manner as in Example 1 (Comparative Example 1.2).

Further, a TlO2 layer containing the catalytically active metal described below was formed in the same manner as in Example 3 (Comparative Example 3.4).

The amount of Tioz layer was both 10% of the filter and the amount of each metal was 2.5% each.

Comparative example 1: C's/Cu/La Comparative example 2:
Cs/Cu/Ce Comparative Example 3: K/Cu/La Comparative Example 4: K/Cu/Ce Regarding the obtained purification material, the pressure loss, regeneration temperature, and N[]X removal rate were determined in the same manner as in Example 1. I asked for it.

The results are shown in Table 1.

As is clear from Table 1, the exhaust gas purifying material of this example provides a small pressure loss. Further, even after 10 hours have passed since the start of use, the NOx purification rate is higher than that of each comparative example. Furthermore, the regeneration temperature of the filter at that time (the temperature at which particulates are ignited and burned) was also low, indicating that the exhaust gas was effectively 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 supports a relatively large amount of catalyst on the filter even if the amount of ceramic as a carrier is small.
Pressure loss is reduced, and particulates and NOX can be effectively removed at the same time.

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 suitable for purifying exhaust gas from diesel engines and the like.

Claims (3)

[Claims] (1) A catalyst layer made of a homogeneous mixture of a catalyst made of (a) an alkali metal element, (b) a Cu element and a V element, and (c) a rare earth element, and a ceramic powder carrier on a heat-resistant porous filter. An exhaust gas purifying material comprising: 1 to 20 parts by weight of the catalyst and 1 to 10 parts by weight of the ceramic powder carrier per 100 parts by weight of the filter. (2) The exhaust gas purifying material according to claim 1, wherein the ceramic powder carrier 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.