JPH05146643A - Purification of exhaust gas - Google Patents

Abstract

PURPOSE:To efficiently reduce and remove NOx in exhaust gas by forming a porous ceramic layer having a special specific surface area to the surface of a porous ceramic filter having a specific void and supporting a catalyst on said ceramic layer to form a purifying material and providing the purifying material on the way of an exhaust gas conduit. CONSTITUTION:A porous ceramic layer with a specific surface area of 2m<2>/g or more is formed to the surface of a porous ceramic filter with a void of 20-90% and a catalyst consisting of an alkali metal element and an element selected from Cu, Co and the like is supported on the porous ceramic layer. In this case, the porous ceramic layer is set to 5-20% by wt. of the filter and the catalyst is set to 0.05-3% by wt. of the porous ceramic layer. This gas purifying material is provided on the way of an exhaust gas passage and liquid hydrocarbon is added to exhaust gas on the upstream side of the purifying material and the temp. of the exhaust gas passing through the purifying material is held to 200-500 deg.C. By this method, NOx is effectively removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification method capable of effectively reducing and removing nitrogen oxides in exhaust gas discharged from various combustion engines.

[0002]

2. Description of the Related Art Exhaust gas discharged from internal combustion engines such as automobile engines, various external combustion engines and combustion equipment such as factories contains nitric oxide,
Nitrogen dioxide and other nitrogen oxides (hereafter referred to as NOx) and particulate carbonaceous substances are contained, and these are becoming a problem as they pollute the environment. In particular, NOx is considered to be one of the causes of acid rain, and the aim is to establish an effective removal method.

As a method for removing NOx in exhaust gas, there is a method using a so-called three-way catalyst for exhaust gas from a gasoline engine, for example. Further, for exhaust gas from a large-scale fixed combustion device (large-scale combustor in a factory, etc.), a metal oxide catalyst such as V ₂ O ₅ is used, and ammonia is introduced as a reducing agent to reduce NOx. The selective catalytic reduction method has been adopted.

However, the above-mentioned three-way catalyst system is efficient for exhaust gas with a relatively high oxygen concentration, such as exhaust gas emitted from a diesel engine or exhaust gas from a so-called lean gasoline engine. It is not possible to remove good NOx. In addition, the method of reducing and removing NOx by mixing ammonia in exhaust gas has problems that ammonia is expensive, that ammonia has toxicity, and that the size of the device is generally large. It is not applicable to the exhaust gas source.

Therefore, the establishment of a new method for reducing (removing) NOx in exhaust gas having a relatively high oxygen concentration is desired, and various attempts have been made so far.

For example, copper-containing zeolite and Al ₂
A method of reducing NOx by adding a hydrocarbon having a small carbon number to exhaust gas using a catalyst such as O ₃ has been proposed (S
AE Technical paper 900496, 1990, JP-A-63-
100919 etc.). However, this method is not practical because there are still problems in NOx reduction characteristics when oxygen concentration is high and durability.

There is also a method of introducing a hydrocarbon into the exhaust gas and reducing and removing NOx in the exhaust gas by the hydrocarbon. As an example thereof, Japanese Examined Patent Publication No. 44-13002 discloses that a honeycomb-shaped ceramic filter carrying a platinum group catalyst allows exhaust gas to flow while controlling the temperature and the flow rate, and a gaseous reducing fuel (specifically, methane or the like). ) Is disclosed.

However, this method is not sufficient for efficiently reducing NOx in the exhaust gas of a diesel engine or the like. According to the research conducted by the present inventors, even if a low carbon number hydrocarbon (methane, propane, etc.), which becomes gaseous in a standard state, is added to the exhaust gas of a diesel engine as a NOx reducing agent, NOx having such a large amount is generated. It was found that the removal rate could not be obtained.

Further, a hydrocarbon is mixed with the exhaust gas containing oxygen and NOx, and the oxygen and the hydrocarbon are reacted with each other to partially oxidize the hydrocarbon to modify it into reducing hydrogen and carbon monoxide. In addition to reducing the amount, the generated modified gas is reacted with NOx contained in the exhaust gas to decompose it into nitrogen, carbon dioxide gas and water (Japanese Patent Laid-Open No. Sho 122-122474).
No.), but with this method, the NOx reduction reaction is performed at 600 ° C.
It has to be performed at a relatively high temperature, and is not suitable for purifying exhaust gas from automobiles.

As another method, a petroleum-based fuel as a reducing agent is added alone or diluted with a part of the combustion exhaust gas or with air and a part of the combustion exhaust gas to a high temperature portion of the combustion exhaust gas, and air is added downstream thereof. To reduce NOx in flue gas by adding methane, propane, methane, propane, so that the ratio (residual oxygen amount in flue gas / oxygen amount required for complete combustion of petroleum-based fuel to be added) falls within a specific range. There is a method for reducing NOx by adding petroleum-based fuel such as gasoline, kerosene, naphtha, and heavy oil in multiple stages to reduce NOx (Japanese Patent Laid-Open No. 54-7916).
No. 1).

However, in this method, the reducing agent and NO
Unless the site that reacts with x is kept at 1000 ° C or higher, NOx cannot be effectively removed, which is also not suitable for exhaust gas purification of automobiles.

Therefore, an object of the present invention is to reduce NOx contained in exhaust gas having a relatively high oxygen concentration and almost no particulates, such as that found in exhaust gas of diesel engines, to the actual exhaust gas of automobiles. An object of the present invention is to provide an exhaust gas purification method that can be effectively removed at a relatively low temperature such as a temperature.

[0013]

As a result of earnest research in view of the above problems, the present inventors have found that a porous ceramic layer having a specific surface area is formed on the surface of a filter made of a porous ceramic having a specific porosity. And form an exhaust gas purifying material in which a catalyst made of a specific metal element is supported on the porous ceramic layer in the middle of the exhaust gas conduit, and add a specific liquid hydrocarbon to the upstream side of the exhaust gas purifying material. If
It was discovered that NOx in exhaust gas can be efficiently reduced and removed. In the exhaust gas having a relatively high oxygen concentration and almost no particulates, it was discovered that the NOx removal rate is improved by reducing the amount of the catalyst supported, and the present invention was completed.

That is, according to the exhaust gas purification method of the present invention, a porous ceramic layer having a specific surface area of 2 m ² / g or more is formed on the surface of a porous ceramics filter having a porosity of 20 to 90%, and Exhaust gas purification in which a porous ceramic layer carries a catalyst comprising (a) an alkali metal element and (b) one or more elements selected from the group consisting of Cu, Co, Mn and V A method of installing a material in the middle of an exhaust gas flow path, adding a liquid hydrocarbon into the exhaust gas on the upstream side of the exhaust gas purifying material to reduce and remove nitrogen oxides in the exhaust gas, wherein the porous ceramic layer Is the filter 5
˜20% by weight, the catalyst is 0.05 to 3.0% by weight of the porous ceramic layer, and the temperature of the exhaust gas passing through the exhaust gas purifying material is kept at 200 to 500 ° C. It is characterized in that nitrogen oxide in the exhaust gas is reduced and removed by using liquid hydrocarbon as a reducing agent.

The present invention will be described in detail below. In the present invention, as the exhaust gas purifying material, a porous ceramic filter having excellent heat resistance, thermal shock resistance and the like, on which a layer of porous ceramic is formed, is used.

First, as the ceramics constituting the filter, alumina, silica, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, mullite, cordierite, etc. may be used. it can. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and composites thereof.

When the exhaust gas passes through the purification material, NOx in the exhaust gas reacts with liquid hydrocarbons added to the exhaust gas (details will be described later) to reduce and remove NOx. In order to effectively proceed with the above, it is necessary to use, as the purifying material, a material having small pores such that the contact area with the gas becomes large. Further, it is necessary to have a porosity such that the pressure loss falls within an allowable range. Therefore, the porosity of the ceramic filter, which is the base material of the purification material, is 20 to
90%. If the porosity is less than 20%, it becomes difficult for the exhaust gas to pass through the purification material, which is not preferable in practice. Further, since the geometric surface area in the purification material becomes small, the NOx reduction reaction cannot be promoted, and the NOx removal rate decreases. On the other hand, 9
If it exceeds 0%, the strength of the purification material decreases and the exhaust gas passes through too easily, so that the NOx removal rate also decreases. Preferably, the porosity is 4
0 to 80%.

The shape and size of the filter can be variously changed according to the purpose. The internal structure may be a foam type, a honeycomb structure type, a three-dimensional mesh structure type made of fibrous refractory, or the like. Considering the ease of manufacturing and the like, it is preferable to use a foam type ceramic filter.

The foam type filter can be formed by various methods, but in particular, Japanese Patent Publication No. 2-502374.
It is preferably formed by the method described in No. In this method, the following foamable composition is used to produce a porous ceramic material. That is, the composition used herein is a foamable composition consisting of an aqueous mixture containing an alkali metal silicate, an alkali metal aluminate, a refractory ceramic material, a viscosity modifying and gel toughening agent, a surfactant and a metal powder. The metal powder is present in an amount sufficient to react with the alkaline substance in the composition, and the alkali metal silicate and the alkali metal aluminate react with each other to form a desired molded body shape. Forming a self-setting alkali metal aluminosilicate hydrogel that serves as a binder for setting a substance, and when an alkaline substance in the composition reacts with the metal powder, hydrogen gas is generated as a by-product, and Before the hydrogen gas set hardens the hydrogel together with the surfactant,
A composition capable of producing a remarkable porosity in the composition.

When a foam type filter is used as a purifying material, one end of the filter, particularly the downstream side, is a high density thin layer part and the other is a low density part within a range of allowable pressure loss. A method of increasing the filter effect can also be used. The low-density portion mentioned here is a portion having the above-mentioned porosity, and the high-density thin layer portion has a porosity of 40 to 85% and a pore size of 3 to 800 μm.
It is preferably about (average 300 μm). Further, the thickness of the high density thin layer portion itself is preferably 0.2 to 2 mm in consideration of pressure loss.

If a filter having such a structure having a low density portion and a high density thin layer portion is used as a purifying material, a good exhaust gas purifying action can be obtained. Because the exhaust gas inlet side has a low density, the exhaust gas easily enters the pores in the filter, and the exhaust gas flowing in the filter receives an appropriate resistance due to the high density thin layer portion on the outlet side. Therefore, the NOx reduction reaction in the relatively low-density filter portion becomes easier to proceed.

There are several methods for forming a high-density thin layer portion on one surface of the foam type filter, but the following method is particularly preferable. (a) A method in which a mold releasing agent composed of glycerin, water and a surfactant is applied to the bottom surface of a mold having a desired shape, a slurry such as cordierite is poured into this mold, the mold is separated, dried and then baked. In this method, the portion in contact with the surface coated with the release agent becomes a high-density thin layer portion. (b) A method in which a uniform filter (a low density portion) is first formed, an organic binder and powders such as cordierite are mixed, and the mixture is applied to one surface of the filter, dried, and fired.

It is to be noted that the filter needs to have practical strength, and therefore, the above-mentioned ceramic material is generally fired at a high temperature of 1000 ° C. or higher to obtain a filter having sufficient strength. The specific surface area (value by the BET method, the same applies below) of the filter material fired in this way is usually 1 m.
^Although it is about ² / g, it is preferable to increase the surface area of the filter in order to effectively purify NOx in the exhaust gas. Therefore, in the present invention, by further providing a porous ceramic layer on the surface of the filter base material described above,
Use an exhaust gas purification material with a large surface area. Unlike the filter material, the porous ceramic layer provided on the surface of the filter does not require high mechanical strength, and thus can be fired at a relatively low temperature to increase the surface area.

The BET specific surface area of the porous ceramic layer provided on the surface of the filter is 2 m ² / g or more. BET
If the specific surface area is less than 2 m ² / g, good NOx cannot be removed. In general, the larger the specific surface area, the more preferable, but the upper limit of the BET specific surface area of the actually formed porous ceramic layer is about 400 m ² / g, so the BET specific surface area of the porous ceramic layer is ² to 400 m ^2. The range is / g.

The thickness of the porous ceramic layer provided on the filter is often limited due to the difference in thermal expansion characteristics between the filter material and the porous ceramic layer. In the present invention, the thickness of the porous ceramic layer provided on the filter is preferably 50 μm or less. With such a thickness, it is possible to prevent the purification material from being damaged by thermal shock or the like during use.

Examples of the porous ceramic layer provided on the filter surface include silica, alumina, titania, zirconia, titania-alumina, silica-alumina, zirconia-alumina, silica-titania, silica-zirconia, titania-zirconia and the like. Be done. In order to reduce NOx more effectively, it is preferable to use an alumina-based ceramic material or a ceramic material such as zirconia, titania, or titania-zirconia that has good NOx reduction ability even when a low molecular weight hydrocarbon is used. ..

There are several methods for forming the porous ceramic layer on the surface of the porous ceramic filter, but the following method is preferable.

First, as a first method, a slurry comprising the above-mentioned ceramic material powder for forming a ceramic layer on the surface, a silica- or alumina-based sol-like binder, and a solvent such as water is prepared. There is a method of forming a porous ceramic layer on the surface of the filter by immersing the filter or passing the slurry through the filter and then firing.

As another method, the filter is dipped in a solution (for example, alcohol solution) of an organic salt of metal (for example, alkoxide) which forms ceramics, and then water vapor is applied to the filter to attach the solution to the surface of the filter. To sol, and further to gel (so-called sol-gel method). Then, there is a method in which the filter is dried and then fired to form a porous ceramic layer serving as a surface layer.

The catalyst supported on the above-mentioned porous ceramic layer is (a) an alkali metal (Li, Na, K, Cs, etc.)
And (b) one or more elements selected from Cu, Co, Mn, and V are used. As the (a) alkali metal, it is particularly preferable to use at least one of sodium, potassium and cesium. Among them, when cesium is used, unburned hydrocarbons remaining in the exhaust gas or liquid hydrocarbons introduced into the exhaust gas on the upstream side of the exhaust gas purification material react well with NOx, resulting in very good NOx Removal can be done. This is because the presence of cesium increases the reaction selectivity between NOx and hydrocarbons,
It is considered that this is because the reaction between oxygen and hydrocarbons in the exhaust gas is suppressed. As the component (b), at least one of the four transition elements Cu, Co, Mn, and V is used as described above, and in particular, the element V is an essential component in the component (b), If at least one of Cu, Co and Mn is added to this, no significant improvement in the initial characteristics of the catalyst can be expected, but stable NOx removal over a long period of time can be obtained.

In addition to the above components (a) and (b),
(c) A catalyst having a structure in which a rare earth element (Ce, La, Nd, Sm, etc.) is added can be used. Thus, by adding the rare earth element (c) to the catalyst, the simultaneous removal characteristics of particulates and NOx can be improved. As the rare earth metal (c), it is preferable to use cerium, lanthanum, neodymium, etc., and it is also possible to use misch metal which is a mixture of rare earth metals.

The amounts of the catalyst components (a), (b) and (c) to be blended are preferably as follows. First, the catalyst is (a)
When it is composed of the component and the component (b), the weight ratio of the respective metal components is (a) 10 to 50% and (b) 50 to 90%.
When (a) is less than 10% by weight and when it exceeds 50% by weight, the reaction characteristics of NOx and hydrocarbons deteriorate. Also especially
(b) at least one of Cu, Co and Mn, and V
When selecting and, it is preferable that the weight ratio of the metal element other than V to the V element is approximately 5/1 to 1/15. Preferably, (a) is 20 to 40%, (b) is 60 to 80%, and the weight ratio of V to at least one of Cu, Co and Mn in (b) is 3/1 to. It is 1/10.

When the catalyst comprises (a), (b) and (c), (a) is 5 to 50%, (b) is 30 to 80%, and (c) is 50%.
It is better to be less than or equal to%. If (a) is less than 5% by weight or more than 50% by weight, the reaction characteristics of NOx and hydrocarbons deteriorate.
If the content of (b) is less than 30% by weight or more than 80% by weight, the reaction characteristics of hydrocarbons and NOx deteriorate. Furthermore, with respect to (c), if the amount exceeds 50% by weight, the NOx reduction reaction by the hydrocarbons introduced into the exhaust gas will not proceed efficiently, so the upper limit is 50%.
Weight% When the catalyst is composed of (a), (b) and (c), the preferable composition is 10 to 30% of (a) and 40 to 70% of (b).
And (c) is 10 to 30%.

By using the exhaust gas purifying material having the catalyst having the above-mentioned structure, NOx can be effectively removed by the liquid hydrocarbon introduced into the exhaust gas. Thus, the reduction of NOx efficiently occurs at a relatively low temperature because the synergistic effects of the simultaneous presence of the liquid hydrocarbons introduced into the exhaust gas, NOx, and the above catalyst components (a) and (b). It seems to be due to the effect.

The amount of the porous ceramic layer supporting the catalyst is 5 to 20% by weight, preferably 10 to 15% by weight of the filter.
And Also, catalytically active species (components (a) to (c) above)
Is 0.05 to 3.0 of the above-mentioned porous ceramic layer.
Weight% If the amount of the catalyst loaded is less than 0.05% by weight with respect to the carrier layer, the effect of loading the catalyst is not significant on the low temperature side, and the NOx purification ability decreases. On the other hand, if the amount of catalyst supported exceeds 3.0% by weight, the NOx removal rate will be greatly reduced. Preferably, the amount of catalytically active species is 0.1 to 2.5% by weight with respect to the supporting layer. In general, when the exhaust gas in which soot (particulate) is hardly present is targeted, in order to increase the reactivity of residual (unburned) hydrocarbons or introduced liquid hydrocarbons with NOx, the above-mentioned composition is used. Although it is preferable to reduce the amount of the catalytically active species, in practice, it is preferable to appropriately adjust the amount within the above-mentioned catalyst loading amount in consideration of engine characteristics (exhaust gas components) and the like.

Next, an exhaust gas purification method of the present invention using the above-mentioned exhaust gas purification material will be described.

In the present invention, the above-mentioned exhaust gas purification material is installed in the middle of the exhaust gas conduit communicating from the engine to the exhaust port. Then, liquid hydrocarbons are added to the exhaust gas at the exhaust gas upstream side portion of the purification material.

The liquid hydrocarbon in the present invention is a hydrocarbon in a liquid state in a standard state and has a boiling point of 90 to 350 ° C.
Refers to the fraction of Specific examples include light oil, cetane and heptane. When a liquid hydrocarbon having a boiling point higher than 350 ° C. is used, the liquid hydrocarbon does not vaporize at the temperature of the exhaust gas under normal engine operating conditions, so the NOx reduction reaction does not proceed so much. Preferably, the boiling point is 160 to
A liquid hydrocarbon having a temperature of 340 ° C. is used. Considering practicality, it is particularly preferable to use light oil.

The amount of liquid hydrocarbon added is preferably 0.2 to 3 in terms of the ratio (weight of liquid hydrocarbon / weight of NOx in exhaust gas) to the amount of NOx contained in exhaust gas. If this ratio is less than 0.2, the effect of adding the liquid hydrocarbon is not significant, and the NOx removal rate decreases. Further, when it exceeds 3, the added liquid hydrocarbon becomes excessive and the liquid hydrocarbon remains in the exhaust gas discharged to the atmosphere.

The liquid hydrocarbon can be added to the exhaust gas by a known method such as spraying.

The temperature of the exhaust gas passing through the exhaust gas purifying material is
Although it needs to be changed a little depending on (the boiling point of) the liquid hydrocarbon used, the temperature is kept at least 200 to 500 ° C. Below this temperature range, the added liquid hydrocarbons are less likely to be gasified, and their decomposition is less likely to occur, and effective reduction of NOx cannot be obtained. Further, when the temperature exceeds this temperature range, the added liquid hydrocarbon itself burns, and the reaction of carbon dioxide and water has priority,
After all, the reduction rate of NOx decreases. When adding light oil, the temperature of the exhaust gas passing through the exhaust gas purifying material should be 300 to 50.
It is better to set it to 0 ° C.

By the way, the actual exhaust gas temperature of an automobile is
It changes every moment depending on the engine operating conditions. So NOx
In order to ensure the purification of the exhaust gas, it is preferable to control the exhaust gas temperature within the above temperature range. As an example of the control, there is the following method. That is, a valve for adjusting the flow rate of exhaust gas is provided upstream of the exhaust gas purification material, the exhaust gas temperature in the exhaust gas purification material is monitored, and when the exhaust gas temperature falls below the above range, the valve is throttled to raise the exhaust gas temperature. When lowering the exhaust gas temperature, the opposite operation to the above operation may be performed.

[0043]

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.

Example 1 Foam type filter comprising cordierite and mullite (apparent volume 0.018 liter, apparent density 0.42)
g / ml, porosity 50%) and alumina powder (average particle size 0.5 μm, specific surface area about 210 m ² / g) 7% by weight,
It was immersed in a slurry composed of 3% by weight of a commercially available alumina sol and 90% by weight of water.

This was taken out from the slurry, dried, and then calcined in the air at 800 ° C. for 3 hours to coat 12% of the weight of the filter with alumina. CuCl ₂ , La (NO ₃ ) ₃ and CsNO ₃ aqueous solutions are used for this filter,
Cu, La and
0.5% when converted to Cs metal alone (wt%, the same below)
After impregnating, drying and firing at 700 ° C., a purification material was obtained.

This exhaust gas purification material was installed in a flow reactor, and a simulated exhaust gas consisting of NOx 800 ppm, oxygen 10%, sulfur dioxide 200 ppm, and the balance nitrogen was passed through the flow reactor at a flow rate of 12 liters / minute. In front of the purification material, add light oil twice the amount of NOx in the exhaust gas (weight ratio), and
The reduction rate of NOx at 0 to 450 ° C was investigated. The results are shown in Figure 1.

Comparative Example 1 A filter used in Example 1 was used as it is as a purifying material without coating the surface of alumina with the same method as in Example 1.
The reduction rate of NOx was measured. The results are shown together with FIG.

Examples 2 and 3 The same filters as those used in Example 1 were immersed in a mixed solution of tetraisopropyl titanate and zirconium-n-propoxide (molar ratio 1: 1), and then reacted with water vapor. And gelation was performed. Then, the filter was dried and then calcined at 700 ° C. to coat 7.5% of the filter weight with the titania-zirconia mixed oxide, and then the same catalytically active species as in Example 1 were added to each of the following:
5% (based on the titania-zirconia composite oxide layer) was carried to obtain an exhaust gas purification material (Example 2). The BET surface area of the titania-zirconia composite oxide that was the surface layer was 41.8 m ² / g.

The same filter as that used in Example 1 was immersed in a mixed solution of aluminum isopropoxide and ethyl silicate (molar ratio 1: 1), and then reacted with water vapor to cause gelation. went. Then, the filter was dried and then calcined at 700 ° C. to coat 4.8% alumina-silica composite oxide based on the weight of the filter, and 0.5% of each of the same catalytically active species as in Example 1 was applied. %
It was supported (on the alumina-silica composite oxide layer) to obtain an exhaust gas purifying material (Example 3). The surface layer of the alumina-silica composite oxide had a BET surface area of 109 m ²
/ G.

Example 1 using these exhaust gas purifying materials
The NOx reduction rate was measured in the same light oil addition amount and temperature range as in. The results are shown together with FIG.

Examples 4 to 14 The filters used in Example 1 were coated with alumina in the same manner as in Example 1. An exhaust gas purifying material carrying the following catalytically active species was produced for this filter in the same manner as in Example 1. Incidentally, in carrying the catalytically active species,
In addition to CuCl ₂ , La (NO ₃ ) ₃ and CsNO ₃ aqueous solutions, CoCl 2
_A mixed solution of ₂ aqueous solutions, manganese acetate, NH ₄ VO ₃ and oxalic acid was used. The loading amount of each element was 0.5% with respect to the alumina coating layer. Example 4: Cs / Cu / Ce Example 5: Cs / Cu Example 6: Cs / Co / La Example 7: Cs / Co / Ce Example 8: Cs / Co Example 9: Cs / Mn / Ce Example 10: Cs / Mn / La Example 11: Cs / V / Ce Example 12: Cs / V / La Example 13: Cs / Mn Example 14: Cs / V

When the NOx reduction rate of each of the above purification materials was measured in the same manner as in Example 1, the NOx reduction rate was found to be approximately the same as the NOx reduction rate in Examples 1 to 3.

Example 15 A foam filter similar to that of Example 1 was coated with alumina in the same manner as in Example 1. CuCl ₂ , La (NO ₃ ) ₃ and CsNO ₃ aqueous solutions are used for this filter,
Cu, La and
0.5% when converted to Cs metal alone (wt%, the same below)
It was impregnated, dried and calcined at 700 ° C. Next, this filter was immersed in a mixed aqueous solution of NH ₄ VO ₃ and oxalic acid, dried, and then fired again at 700 ° C. to obtain a purification material.

This exhaust gas purifying material was installed in the flow reactor in the same manner as in Example 1, and 200 to 4 in the same manner as in Example 1.
The reduction rate of NOx at 00 ° C was investigated. Note that the amount of light oil added before the purification material is 2 times the amount of NOx in the simulated exhaust gas.
Double (weight ratio). The results are shown in Figure 2.

Comparative Example 2 The same procedure as in Example 15 was carried out by using the filter used in Example 15 as a purifying material without coating alumina on the surface.
The reduction rate of NOx was measured. The results are shown in FIG.

Examples 16 and 17 The same filter as that used in Example 15 was immersed in a mixed solution of tetraisopropyl titanate and zirconium-n-propoxide (molar ratio 1: 1), and then reacted with water vapor. And gelation was performed. Then, the filter was dried and calcined at 700 ° C. to coat 7.5% of the filter weight with the titania-zirconia mixed oxide, and then the same catalytically active species as in Example 15 were added to each of the following:
An exhaust gas purifying material was obtained by loading 5% (Example 16). In addition,
BET of titania-zirconia composite oxide which is a surface layer
The surface area was 41.8 m ² / g.

The same filter as that used in Example 15 was dipped in a mixed solution of aluminum isopropoxide and ethyl silicate (molar ratio 1: 1), and then reacted with water vapor to cause gelation. went. Then, the filter was dried and then calcined at 700 ° C. to coat 4.8% alumina-silica composite oxide with respect to the weight of the filter, and 0.5% of each of the same catalytically active species as in Example 15 was added. %
It was carried to obtain an exhaust gas purification material (Example 17). The BET surface area of the alumina-silica composite oxide, which is the surface layer, was 109 m ² / g.

Example 15 was prepared using these exhaust gas purifying materials.
The NOx reduction rate was measured in the same light oil addition amount and temperature range as in. The results are shown in FIG.

Examples 18 to 24 The filters used in Example 15 were coated with alumina in the same manner as in Example 15. An exhaust gas purifying material carrying the following catalytically active species was produced for this filter in the same manner as in Example 15. Incidentally, in carrying the catalytically active species,
In addition to CuCl ₂ , La (NO ₃ ) ₃ and CsNO ₃ aqueous solutions, CoCl 2
_A mixed solution of ₂ aqueous solutions, manganese acetate, NH ₄ VO ₃ and oxalic acid was used. The loading amount of each element was 0.5%. Example 18: Cs / Cu / V / Ce Example 19: Cs / Cu / V Example 20: Cs / Co / V / La Example 21: Cs / Co / V / Ce Example 22: Cs / Co / V Example 23: Cs / Mn / V / Ce Example 24: Cs / Mn / V

When the NOx reduction rate of each of the above purification materials was measured in the same manner as in Example 15, it was found that the NOx reduction rate was substantially the same as the NOx reduction rate in Examples 15 to 17.

As can be seen from the above, the exhaust gas purifying material of this example has much better NOx purification characteristics than the exhaust gas purifying material of the comparative example.

Example 25 The same filter as used in Example 1 was used as an alumina powder (average particle size: 0.5 μm, specific surface area: about 210 m ² / g).
It was immersed in a slurry of 7% by weight, a commercially available alumina sol 3% by weight, and water 90% by weight.

This was taken out of the slurry, dried, and then calcined in the air at 800 ° C. for 3 hours to coat 12% of the weight of the filter with alumina. For this filter, Cu (NO ₃ ) ₂ , La (NO ₃ ) ₃ , and CsNO ₃ aqueous solutions were used.
1%, 1%, and 0.2 in terms of La and Cs metal simple substance
% Impregnated, dried and fired at 700 ° C. to obtain a purification material.

This exhaust gas purifying material was installed in a flow reactor, and a simulated exhaust gas consisting of NOx 800 ppm, oxygen 10%, sulfur dioxide 200 ppm, and the balance nitrogen was passed through the flow reactor at a flow rate of 12 liters / minute. In front of the purification material, add C ₇ H ₁₆ twice the NOx amount in the exhaust gas (weight ratio),
The reduction rate of NOx at 200 to 450 ° C. was investigated. Results are shown in FIG.

As can be seen from FIG. 3, when C ₇ H ₁₆ was added, good removal of NOx was observed between about 370 ° C. and 450 ° C.

[0066]

As described in detail above, according to the method of the present invention, NOx in exhaust gas can be effectively reduced at a relatively low temperature of 500 ° C. or lower.

The method of the present invention is particularly effective for exhaust gas in an oxidizing atmosphere such as found in diesel engine exhaust gas.

[Brief description of drawings]

FIG. 1 is a graph showing NOx reduction rates in Examples 1 to 3 and Comparative Example 1.

2 is a graph showing NOx reduction rates in Examples 15 to 17 and Comparative Example 2. FIG.

FIG. 3 is a graph showing the NOx reduction rate in Example 25.

Claims (5)

[Claims] 1. A porous ceramics layer having a specific surface area of 2 m ² / g or more is formed on the surface of a porous ceramics filter having a porosity of 20 to 90%, and (a) ) An exhaust gas purifying material carrying a catalyst comprising an alkali metal element and (b) one or more elements selected from the group consisting of Cu, Co, Mn and V is provided in the middle of the exhaust gas passage. An exhaust gas purification method, wherein the porous ceramic layer is installed and the liquid hydrocarbon is added to the exhaust gas upstream of the exhaust gas purification material, wherein the porous ceramic layer is 5 to 20% by weight of the filter.
In addition, the catalyst is 0.05 to 3.0% by weight of the porous ceramic layer, and the temperature of the exhaust gas passing through the exhaust gas purifying material is maintained at 200 to 500 ° C. to remove the liquid hydrocarbons. A method for purifying exhaust gas, which comprises reducing and removing nitrogen oxides in the exhaust gas as a reducing agent. 2. The exhaust gas purification method according to claim 1, wherein the catalyst further contains (c) a rare earth element. 3. The exhaust gas purification method according to claim 1, wherein the component (b) of the catalyst is a V element, Cu, Co,
And an exhaust gas purification method comprising one or more elements selected from Mn. 4. The exhaust gas purification method according to claim 1, wherein light oil is used as the liquid hydrocarbon, and the exhaust gas temperature is maintained at 300 to 500 ° C. 5. The exhaust gas purification method according to claim 1, wherein the amount of the liquid hydrocarbon added to the exhaust gas is (weight of the liquid hydrocarbon / nitrogen oxide in the exhaust gas). The exhaust gas purification method is characterized in that the weight ratio is 0.2 to 3.