JPH04363120A - Exhaust gas purifying material and method for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain an exhaust gas purifying material by which NOx in exhaust gas discharged from a diesel engine, etc., under a considerable change in the concn. of oxygen can be reduced and removed with hydrocarbon (HC). CONSTITUTION:A catalyst is supported on a porous ceramic layer formed on a heat resistant porous filter to obtain an exhaust gas purifying material. The catalyst consists of an alkali metal and one or more of Cu, Co, Mn and V. The amt. of the ceramic layer is 3-15wt.% of the amt. of the filter. The amt. of the catalyst is 0.05-2.0wt.% of the amt. of the ceramic layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an exhaust gas purifying material and an exhaust gas purifying method using this exhaust gas purifying material, and more specifically to nitrogen oxides (
The present invention relates to an exhaust gas purification material that can reduce and remove NOx (hereinafter referred to as NOx) using hydrocarbons, and an exhaust gas purification method using the exhaust gas purification material.

0002

[Prior art and problems to be solved by the invention] In recent years,
NOX in exhaust gas emitted from diesel engines, etc.
Particulate carbon materials (mainly composed of solid carbon particles, called particulates) have become a problem as they are harmful to environmental health. In particular, NOx is considered to be one of the causes of acid rain and is a major environmental problem.

As a method for removing NOx from exhaust gas, for example, a so-called three-way catalyst is used for exhaust gas from gasoline engines, etc., and NOx is converted into harmless N2.
A method is being adopted to reduce the However, in general, the reduction reaction of NOx is difficult to proceed in an atmosphere with a high oxygen concentration, and it can be said that the method using this three-way catalyst is insufficient.

Under these circumstances, various catalysts aimed at effectively removing NOx are being actively researched and developed. For example, Japanese Patent Application Laid-Open No. 63-100919 discloses that by using a catalyst containing copper and bringing exhaust gas containing nitrogen oxides into contact with the catalyst in the presence of hydrocarbons in an oxidizing atmosphere, nitrogen in the exhaust gas is reduced. A method for removing oxides is disclosed. However, according to the research conducted by the present inventors, conventional catalysts such as those mentioned above are inferior in durability and purification characteristics when oxygen concentration is high, and have poor NO
It is not possible to remove x. Also, JP-A-3-1
No. 6645 contains (a) alkali metals, and (b) groups IB, IIB, VA, VIA, and VIIA of the periodic table.
group, group VIII transition metals excluding platinum group elements, and Sn
Disclosed is an exhaust gas purifying material having a catalyst comprising one or more elements selected from the group consisting of: This catalyst can ignite and burn particulates in exhaust gas at a relatively low temperature. However, according to the research conducted by the present inventors, it has been found that it is not possible to efficiently remove NOx from exhaust gas that contains almost no particulates unless the types of elements constituting the catalyst and their amounts are limited. Ta.

Therefore, an object of the present invention is to provide an exhaust gas purification material and an exhaust gas purification method that can reduce and remove NOx contained in exhaust gas with large changes in oxygen concentration, such as those emitted by diesel engines, using hydrocarbons (HC). The goal is to provide the following.

[0006]

[Means for Solving the Problems] As a result of extensive research into the purification of exhaust gas containing hydrocarbons and NOx, the present inventors have found that, basically, alkali metal elements and specific transition metal elements have been purified. This catalyst system is effective, but when a relatively large amount of hydrocarbons is present in the exhaust gas, the inventors discovered that reducing the amount of catalyst actually improves the NOx removal rate, and completed the present invention.

That is, in the exhaust gas purifying material of the present invention in which a catalyst is supported on a porous ceramic layer provided on a heat-resistant porous filter, the catalyst comprises (a) an alkali metal element, and (b) Cu, Co , Mn, and V, the porous ceramic layer is 3 to 15% by weight of the filter, and the catalyst is the porous ceramic layer. 0.0 of layer
It is characterized by being 5 to 2.0% by weight.

Furthermore, the exhaust gas purification method of the present invention is characterized in that nitrogen oxides are reduced using hydrocarbons in the exhaust gas as a reducing agent using a catalyst supported on the filter.

The present invention will be explained in detail below. The filters that serve as the base material for exhaust gas purification materials are porous, heat resistant,
In particular, use one with high thermal shock resistance. Further, it is necessary that the pressure loss is within an allowable range and that particulate collection performance is maintained. Such filter forming materials include alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia,
Examples include ceramics such as titania-zirconia, mullite, and cordierite.

[0010] As the filter, a known honeycomb type or foam type filter can be used. The shape and size of the filter can be changed in various ways depending on the purpose, but when using a foam type filter, it is generally formed into a cylindrical shape, with a diameter of 30 to 400 mm and a thickness of 50 mm. ~
Preferably, the length is 300 mm. Also, if necessary,
A plurality of sheets may be stacked. In addition, when using a foam type filter, it is preferable that its porosity is 40 to 80% and the average pore diameter is about 200 to 400 μm.

The catalysts supported on the above filter via the porous ceramic layer include (a) alkali metals (Li, Na, K, Cs, etc.), and (b) Cu, C.
One or more elements selected from o, Mn, and V are used. (a) As the alkali metal, it is particularly preferable to use at least one of sodium, potassium, and cesium. Among them, when cesium is used, many unburned HCs, including saturated hydrocarbons such as propane, are also converted to NOx.
As a result, very good NOx removal can be achieved. This is due to the presence of cesium.
This is thought to be because the reaction selectivity between oxygen and hydrocarbons increases, and the reaction between oxygen in the exhaust gas and hydrocarbons is suppressed. In addition, as the component (b), as mentioned above, Cu,
At least one of the four transition elements Co, Mn, and V is used, and in particular, the V element is an essential component in component (b), and at least one of Cu, Co, and Mn is added thereto. With this configuration, although it is not expected that the initial characteristics of the catalyst will be significantly improved, stable NOx removal over a long period of time can be obtained.

[0012] In addition to the above components (a) and (b), (c) rare earth elements (Ce, La, Nd, S
m, etc.) can be used. When the rare earth element (c) is added to the catalyst in this way, the particulates present in the exhaust gas also act as a reducing agent, making it possible to reduce and remove NOx. (c) As the rare earth metal, cerium, lanthanum, neodymium, etc. are preferably used, and misch metal, which is a mixture of rare earth metals, can also be used.

The amounts of each of the above catalyst components (a), (b) and (c) are preferably as follows. First, when the catalyst consists of component (a) and component (b), the weight ratio of each metal component is 10 to 5.
0%, (b) 50-90%. When (a) is less than 10% by weight and when it exceeds 50% by weight, the reaction characteristics of NOx and HC deteriorate. Also,
In particular, when selecting at least one of Cu, Co, and Mn and V as (b), the ratio of the metal element other than V to the V element is about 5/1 to 1/15 by weight. It is better to

[0014] Further, the catalyst is (a), (b) and (c
), (a) is 5-50%, (b)
is preferably 30 to 80%, and (c) is preferably 50% or less. When (a) is less than 5% by weight or more than 50% by weight, the reaction characteristics between NOx and HC deteriorate. (b) is 3
Less than 0% by weight or more than 80% by weight, HC and NOx
The reaction properties of Furthermore, regarding (c), if it exceeds 50% by weight, the reduction reaction with NOx particulates and HC will not proceed efficiently, so the upper limit is set to 50% by weight.

[0015] By using an exhaust gas purifying material having a catalyst configured as described above, NOx can be effectively removed. In other words, within the filter of the exhaust gas purification material,
When HC coexists with the catalyst element and oxygen, HC acts as a reducing agent to reduce NOx, and the exhaust gas is effectively purified. The reason why NOx reduction occurs efficiently at a relatively low temperature is believed to be due to the synergistic effect of the simultaneous presence of HC and the above-mentioned catalyst components (a) and (b). In addition, when a catalyst containing (c) in addition to (a) and (b) is used, particulates in exhaust gas can be ignited and burned at a relatively low temperature, and particulates can be It also acts as a reducing agent and reduces NOx.

[0016] Incidentally, exhaust gas from a diesel engine or the like normally contains about 100 to 300 ppm of unburned HC, but this HC includes propane, propylene,
Contains acetylene, ethylene, etc. In the catalysts proposed so far in which Cu exists alone as a catalytically active species (for example, JP-A-63-100919), unburned HC has unsaturated bonds such as propylene and acetylene. In some cases, this HC is used as a reducing agent to reduce NOx.
However, the reaction activity using saturated hydrocarbons such as propane as a reducing agent is low, and the
Reductive removal of Ox cannot be said to be sufficient. however,
By using a catalyst with the composition described above, it becomes possible to efficiently reduce NOx even with saturated hydrocarbons such as propane as a reducing agent, resulting in significantly superior NOx purification compared to conventional catalysts. It can be performed.

The above catalyst is supported on the heat-resistant porous filter after a carrier layer made of ceramics which is more porous and has a larger surface area than the filter is formed on the filter. As the material for forming the carrier layer, porous ceramics having a large surface area such as titania, alumina, zirconia, magnesia, titania-alumina, titania-silica, silica-zirconia, and alumina-silica are used. In particular, when increasing the reactivity between HC and NOx, it is preferable to use a carrier layer made of zirconia, titania, alumina, titania-zirconia, or alumina-zirconia.

[0018] The amount of carrier layer is, in the case of ceramic filters, between 3 and 15% by weight of the filter, preferably between 5 and 12%. In addition, the catalytically active species are the sum of ((a) +
(b) or (a) + (b) + (c)) is 0.05 to 2.0% by weight of the carrier layer. If the amount of catalyst supported is less than 0.05% by weight based on the carrier layer, the effect of supporting the catalyst will not be significant, and the ability to purify HC and NOx will decrease. On the other hand, if the supported amount of catalyst exceeds 2.0% by weight, the NOx removal rate will decrease, so the upper limit should be set at 2.0% by weight.
0% by weight. Generally speaking, in order to improve the combustion characteristics of soot (particulates), it is better to increase the amount of catalytic active species, and to increase the reactivity of HC and NOx, it is better to use a smaller amount of catalytic active species. Therefore, it is preferable to adjust the supported amount of catalyst appropriately within the above-mentioned range in consideration of engine characteristics (exhaust gas components), etc.

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.

[0020] Furthermore, the formation of the carrier layer by the sol-gel method is carried out 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 titania (TiO2) is used as the ceramic for the carrier layer, first a Ti alkoxide (e.g., Ti(O-
CH
3. A coating liquid is produced by adding acids such as COOH, HNO3, and HCl. After immersing the filter in this coating liquid and pulling it out, it is reacted with steam or water to form a gel. 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 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, aluminum alkoxide is used in the same manner as in the case of titania described above. The same applies when using other porous carriers.

[0022] After forming a porous carrier layer made of ceramics on the filter by the above-mentioned wash coat method or sol-gel method, next, catalytically active species such as carbonate, nitrate, acetate, hydroxide, etc. The carrier layer is impregnated with an aqueous solution of , dried and calcined again to support the catalyst. In addition, as salts of catalytically active metal species, as long as they are soluble in water,
As mentioned above, any type of salt such as carbonate, nitrate, acetate, hydroxide, etc. can be used. For supporting V, a solution of NH4VO3 and oxalic acid can be used. Furthermore, an alkali metal and V can be simultaneously supported using an alkali vanadate.

In the method of the present invention, NOx in the exhaust gas is reduced and removed by HC using the above-mentioned exhaust gas purifying material. Since HC in the exhaust gas mainly consists of methane, ethylene, acetylene, etc., the NOx reduction temperature is 200°C. ~5
00°C, preferably 250-450°C. If the reaction temperature is too high, combustion of HC itself will occur, reducing the NOx reduction properties. In addition, in the method of the present invention, when there is little HC that acts as a reducing agent in the exhaust gas, NOx
It is also possible to forcibly introduce HC such as ethylene, propane, propylene, etc. in an amount necessary and sufficient to reduce the .

[0024]

EXAMPLES The present invention will be explained in more detail with reference to the following specific examples. Example 1 Cordierite ceramic foam (apparent volume 2
The filter was coated with 10% (weight %, same hereinafter) of TiO2-ZrO2 by wash coating method. Using an aqueous solution of CuCl2, La(NO3)3 and CsNO3 on the obtained filter, these compounds were treated with T.
iO2 - ZrO2 was impregnated with 0.5% of Cu, La and Cs in terms of metal element, and after drying,
It was fired at 700°C to obtain a purifying material. Note that in this purifying material, Cu, La, and Cs exist as oxides.

[0025] Regarding this purifying material, the displacement is 510 cc.
Using a diesel engine, the conversion rate of NOx was determined when the temperature inside the exhaust gas purifying material was 400°C. The engine was operated at a rotation speed of 1500 rpm and a load of 90
%. Under these operating conditions, HC in the exhaust gas is 200 ppm in total of all hydrocarbons, CO is 460 ppm, and NOx
was 480 ppm, O2 was 10%, and SO2 was 200 ppm. The results are shown in Table 1.

Examples 2 to 12 TiO2 − was applied to the foam filter in the same manner as in Example 1.
Coated with 10% ZrO2, CuCl2, Ce(N
C using aqueous solutions of O3 ) 3 and CsNO3
The TiO2-ZrO2 layer was impregnated with u, Ce and Cs at 0.5% each, dried and fired in the same manner as in Example 1 to obtain a purifying material supporting a catalyst consisting of Cu, Cs and Ce. Example 2).

Similarly, using aqueous solutions of CuCl2 and CsNO3, Cu and Cs were respectively converted to TiO2 -
A purification material carrying 0.5% of ZrO2 was obtained (
Example 3).

Furthermore, in the same manner as in Example 1, the filter was coated with 10% Al2O3, and CuCl2
and CsNO3 aqueous solution, Cu and Cs were added at 0.00% each.
A purification material with a loading of 5% was obtained (Example 4).

Furthermore, in place of CuCl2, Co
A purifying material having the following catalytically active species was prepared in the same manner as in Example 1 or 2 using Cl2 or manganese acetate. In addition, as the porous ceramic layer provided on the filter, Al2O3 was used in Examples 8 and 11, ZrO2 was used in Examples 10 and 12, and TiO2-Z was used in the other examples.
rO2 was used. The amount of porous ceramic layer in each purifying material is 10% relative to the foam filter.
And so. The amount of each catalytically active species was set such that each metal component was 0.5%. Catalytic active species (ceramic layer) Example 2: Cs/Cu/Ce (TiO2 -ZrO2
) Example 3: Cs/Cu (TiO2-ZrO2) Example 4: Cs/Cu (Al2 O3) Example 5: Cs
/Co/La(TiO2-ZrO2) Example 6:C
s/Co/Ce (TiO2-ZrO2) Example 7:
Cs/Co(TiO2-ZrO2) Example 8: Cs
/Co(Al2O3) Example 9: Cs/Mn/La
(TiO2-ZrO2) Example 10: Cs/Mn/
Ce(ZrO2) Example 11: Cs/Mn(Al2
O3) Example 12: Cs/Mn(ZrO2)

00
30 For each of the obtained purifying 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 Example 1 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,
A purification material carrying 0.5% Cu was prepared using a CuCl2 aqueous solution. The method of supporting Cu element was the same as in Example 1.

[0032] Regarding the obtained purifying material, the regeneration temperature and NOx removal rate were determined in the same manner as in Example 1. The results are shown in Table 1.

Table 1 Example No. NOx purification rate (1
) Example 1 60 Example 2
50 Example 3
60 Example 4 50 Example 5 50 Example 6
40 Example 7
50 Example 8 40 Example 9
45 Example 10
40 Example 11
45 Example 12 40 Comparative Example 1
15 Table 1 Note (1): NOx purification rate (%) calculated from the amount of NOx in the exhaust gas before and after passing through the filter

As is clear from Table 1, the exhaust gas purification materials of each example have a high NOx purification rate of 40% or more.

Example 13 Cordierite ceramic foam (apparent volume 2
The filter was coated with 10% (weight %, same hereinafter) of TiO2-ZrO2 by wash coating method. The obtained filter was impregnated with 0.5% of each of Cu, La, and Cs based on TiO2-ZrO2 using aqueous solutions of CuCl2, La(NO3)3, and CsNO3, dried, and then fired at 700°C. Next, the filter obtained above was immersed in a mixed aqueous solution of NH4 VO3 and oxalic acid to impregnate it with 0.5% V, and then soaked again at 700% V.
The mixture was fired at ℃ for 3 hours to obtain a purifying material.

[0036] Regarding this purifying material, the displacement is 510 cc.
Using a diesel engine, the conversion rate of NOx was determined when the temperature of the filter in the exhaust gas purifying material was 400°C. The conversion rate of NOx was determined at the beginning of the use of the purifying material (when a decrease in pressure loss was observed for the first time) and at the time when 10 hours had passed since the use of the purifying material. The engine was operated at a rotation speed of 1500 rpm and a load of 90%.
And so. Under these operating conditions, HC in the exhaust gas is 200 ppm in total of all hydrocarbons, CO is 460 ppm, and NOx
was 480 ppm, O2 was 10%, and SO2 was 200 ppm. The results are shown in Table 2.

Examples 14 to 24 In the same manner as in Example 13, TiO2-ZrO2 (Example 14) was added to the foam filter used in Example 13.
, 15, 17, 18, 21 and 22), Al2 O3 (
Examples 16, 20 and 24), ZrO2 (Example 19)
, 23), respectively, and coated with CuCl2, CoCl2 aqueous solution or manganese acetate aqueous solution, La(NO3)3 or Ce(NO
3) A purification material supporting the catalyst shown below was prepared in the same manner as in Example 13 using a 3 aqueous solution, a KCl or CsNO3 aqueous solution, and an NH4 VO3 aqueous solution. The supported amount of each metal component is 0.2% each for rare earth elements and 0.5% each for other elements in each ceramic layer.
%.

Catalytic active species (ceramic layer) Example 1
4: Cs/Cu/Ce/V (TiO2-ZrO2)
Example 15: Cs/Cu/V(TiO2-ZrO2
) Example 16: Cs/Cu/V(Al2O3) Example 17: Cs/Co/La/V(TiO2-ZrO2
) Example 18: Cs/Co/Ce/V(TiO2 −
ZrO2) Example 19: Cs/Co/V(ZrO2
) Example 20: Cs/Co/V(Al2O3) Example 21: Cs/Mn/La/V(TiO2-ZrO2
) Example 22: Cs/Mn/Ce/V(TiO2 −
ZrO2) Example 23: Cs/Mn/V(ZrO2
) Example 24: Cs/Mn/V (Al2O3)

0
[039] For each of the obtained purifying materials, the regeneration temperature and NOx purification rate were determined in the same manner as in Example 13. The results are shown in Table 2.

Comparative Example 2 A cordierite foam filter similar to that in Example 13 was used, and 10% TiO2 was supported on the filter by the wash coating method. A purifying material carrying 0.5% Cu was prepared using a CuCl2 aqueous solution for the obtained filter. The method of supporting Cu element was the same as in Example 13.

[0041] Regarding the obtained purifying material, the regeneration temperature and NOx removal rate were determined in the same manner as in Example 13. Table 2 shows the results.
shown according to

[0042]
Table 2
Early (1)
10 hours later (2)
Example No. NOx purification rate (3)
NOx purification rate (3)
Example 13 45
42
Example 14 40
40
Example 15 4
5 42
Example 16
40 38
Example 17
35 32
Example 18
30 28
Example 1
9 35
32 Example 20 30
28
Example 21 35
32
Example 22 30
28
Example 23 35
32
Example 24
35 33
Comparative example 2
15 8
Table 2 Note (1): The point at which the first decrease in pressure loss was observed. (2): When the pressure loss decreases 10 hours after gas starts passing through the filter. (3): NO in exhaust gas before and after passing through the filter
NOx purification rate (%) calculated from x amount

As is clear from Table 2, Examples 13 to 2
The exhaust gas purification material No. 4 has an extremely good NOx purification rate even after 10 hours of use.

[0044]

Effects of the Invention As explained above, if the exhaust gas purifying material of the present invention is used, NOx can be reduced by using HC in the exhaust gas as a reducing agent.
By reducing NOx, NOx can be efficiently removed.

[0045] The exhaust gas purifying material supporting a catalyst consisting of (a) an alkali metal element, (b) at least one of Cu, Co, Mn or V, and (c) a rare earth element is The particulates inside can also be used as reducing agents to purify NOx.

[0046] Furthermore, the exhaust gas purifying material having the catalyst containing V as the component (b) has the following properties:
Simultaneous removal of NOx and HC can be achieved effectively over a long period of time.

In the purifying material of the present invention, a porous ceramic layer is first formed on a filter by a wash coat method, a sol-gel method, etc., and a catalyst is supported on the ceramic layer. The catalyst is supported at a uniform concentration, resulting in good exhaust gas purification performance.

[0048] The purifying material of the present invention is capable of removing unburned HC and NO
It is suitable for purifying exhaust gas containing x and can efficiently purify exhaust gas from diesel engines and the like.

Claims (6)

[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)
The porous ceramic layer is composed of one or more elements selected from the group consisting of Cu, Co, Mn and V, and the porous ceramic layer accounts for 3 to 15% by weight of the filter,
The catalyst has a content of 0.05 to 2.0% in the porous ceramic layer.
An exhaust gas purifying material characterized by having a content of 0% by weight. 2. The exhaust gas purifying material according to claim 1, wherein the catalyst further contains (c) a rare earth element. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the component (b) of the catalyst comprises V element, Cu,
An exhaust gas purifying material comprising one or more elements selected from Co and Mn. 4. The exhaust gas purifying material according to claim 1, wherein the ceramic layer is made of Al2O3.
, Al2O3-based composite oxide, TiO2, ZrO
An exhaust gas purifying material comprising either TiO2 or TiO2-ZrO2. 5. The exhaust gas purifying material according to claim 1, wherein the alkali metal element (a) is Cs. 6. A method of purifying exhaust gas using the exhaust gas purifying material according to any one of claims 1 to 5, comprising:
An exhaust gas purification method characterized in that nitrogen oxides are reduced and removed by using a catalyst supported on the filter using hydrocarbons in the exhaust gas as a reducing agent.