JPH05245381A - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purifying material capable of reducing and removing NOX in an exhaust gas at a relatively low temp. even in an oxidizing exhaust gas contg. an extremely small amt. of particulate carbon material and a small amt. of combustibles such as unburned hydrocarbons as seen in the exhaust gas from a gasoline engine with the air-to-fuel ratio on the lean side. CONSTITUTION:A first catalyst consisting of one or >=2 kinds of elements selected from (a) one or >=2 kinds of alkali metal elements, (b) groups IB, IIB, VA, VIA, VIIIA and VIII of the periodic table (except platinum elements transition metals and Sn is deposited on the inlet side of a heat-resistant porous formed body, and a second catalyst consisting of one or >=2 kinds of platinum elements on the outlet side, and the exhaust gas purifying material is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material and an exhaust gas purifying method using the exhaust gas purifying material. More specifically, even in the exhaust gas containing almost no particulate carbonaceous substance and having an oxidizing atmosphere, The present invention relates to an exhaust gas purifying material capable of effectively purifying harmful gas components such as existing nitrogen oxides, and an exhaust gas purifying method using the same.

[0002]

2. Description of the Related Art Exhaust gas emitted from internal combustion engines such as automobiles, various external combustion engines, combustion equipment installed in factories, etc.
It is called NOx), but this NOx is one of the causes of acid rain, which is a major environmental problem.

As a method for removing NOx in exhaust gas,
For example, for NOx in the exhaust gas from a gasoline engine, a method is adopted in which the air-fuel ratio during engine operation is adjusted and NOx is reduced to harmless N ₂ by using a so-called three-way catalyst. However, in general, in an atmosphere with a high oxygen concentration, NO is introduced without introducing a reducing gas.
The reduction reaction of x is difficult to proceed. For example, under the condition that the amount of oxygen in the exhaust gas of a gasoline engine, etc., where the air-fuel ratio becomes lean side becomes excessive, it is not possible to reduce NOx by the conventional three-way catalyst system. difficult.

On the other hand, with respect to factory exhaust gas, a method of reducing NOx by using NH ₃ as a reducing agent using an oxide catalyst is used, but there is a drawback such as an increase in size of the device. Not suitable for moving exhaust gas sources such as automobiles.

Further, it is possible to reduce NOx in the presence of an appropriate catalyst by using a particulate carbon material (generally called "particulate") in exhaust gas as a reducing agent. Very little particulate carbon material is available and this method cannot be used.

Therefore, recently, a catalyst capable of effectively removing NOx and a removing method using them have been vigorously researched and developed.

For example, JP-A-63-100919 and SAE T
echnical Paper (900496, 1990) uses catalysts such as zeolite and alumina containing copper, by contacting exhaust gas containing nitrogen oxides with the catalyst in the presence of hydrocarbons in an oxidizing atmosphere. A method for removing nitrogen oxides in exhaust gas is disclosed.

However, the conventional catalysts and methods including the above-mentioned catalysts and methods are not practical because there are problems in catalytic properties and durability when the oxygen concentration in the exhaust gas is high. ..

Therefore, the object of the present invention is to reduce the amount of particulate carbonaceous matter and to combustible hydrocarbons such as unburned hydrocarbons (hereinafter referred to as HC) as seen in the exhaust gas of a gasoline engine whose air-fuel ratio is lean. Even in exhaust gas with a small amount of organic substances (that is, even in an oxidizing atmosphere),
An exhaust gas purification material and an exhaust gas purification method capable of effectively reducing and removing NOx at a relatively low temperature.

[0010]

As a result of earnest research in view of the above problems, the present inventor has found that the heat-resistant porous molded body contains an alkali metal and a specific transition metal at the same time in the exhaust gas inlet side. NOx in the exhaust gas in an oxidizing atmosphere that does not substantially contain particulate carbon substances such as exhaust gas from a gasoline engine etc. by supporting the catalyst and supporting the catalyst composed of a platinum group element on the exhaust gas outlet side part The present invention has been completed by discovering that it is possible to efficiently purify harmful substances such as.

That is, the exhaust gas purifying material of the present invention, which contains almost no particulate carbonaceous material and purifies the exhaust gas which becomes an oxidizing atmosphere, has the following features:
(a) from one or more alkali metal elements, and (b) a transition metal of Group VIII, IIB, VA, VIA, VIIA, or VIII other than the platinum group of the periodic table, and Sn. A first catalyst composed of one or more elements selected from the group consisting of is supported, and the outlet side portion of the molded body is composed of one or more platinum group elements. A second catalyst is supported.

Further, the exhaust gas purifying method of the present invention which uses the above exhaust gas purifying material and purifies exhaust gas which does not contain particulate carbon material and becomes an oxidizing atmosphere, is a reducing agent for removing unburned hydrocarbons present in the exhaust gas. Is characterized by reducing nitrogen oxides.

When the amount of unburned hydrocarbons is small, NOx
Introduce hydrocarbons such as propane and propylene necessary for reducing nitrogen oxides to reduce nitrogen oxides in the range of 200 to 500 ° C.

[0014]

The present invention will be described in detail below. Since the molded product used in the present invention allows high temperature exhaust gas to pass therethrough, it must be porous and have excellent heat resistance, particularly thermal shock resistance. Examples of the material for forming such a molded body include alumina, silica, zirconia, titania, and their composites such as silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, Examples include ceramics such as mullite and cordierite.

As the molded body made of the above material, it is preferable to use a honeycomb type or foam type filter having a small pressure loss, but a pellet type filter can also be used.

In the present invention, (a) an alkali metal element (Li,
Na, K, Cs, etc.), and (b) I of the periodic table.
B group, IIB group, VA group (V, Nb, Ta), VIA group (Cr, Mo,
W), a VIIA group (Mn, Tc, Re), a transition metal of the VIII group excluding the platinum group, and a first catalyst comprising one or more elements selected from the group consisting of Sn, and A second catalyst composed of a platinum group element is used.

The first catalyst is (a) an alkali metal element (L
(i, Na, K, Cs, etc.), and (b) Group IB, IIB, VA (V, Nb, Ta), VIA (Cr,
Mo, W), VII Group A (Mn, Tc, Re), VI excluding platinum group
It is composed of one or more elements selected from the group consisting of Group II transition metals and Sn. In particular, K is used as the component (a).
And / or Cs, and as the component (b), it is preferable to use one or more elements of Cu, Co and Mn.
Further, it is preferred to use V in combination with Cu, Co, Mn or the like as the component (b).

The above-mentioned first catalyst reduces NOx by using HC in the exhaust gas as a reducing agent at a relatively low temperature. That is,
Due to the presence of the above catalyst, HC is activated and reacts with NOx even at a relatively low temperature of about 200 to 500 ° C., and NOx is efficiently reduced to N ₂ . It is considered that the reduction of NOx at a relatively low temperature is due to the synergistic effect of the simultaneous presence of NOx and HC in the exhaust gas and the above catalyst components (a) and (b).

When Cu, Co, or Mn is used as the component (b), its purifying ability is excellent at the initial stage of use, but the catalyst is gradually purified due to the presence of sulfur and its oxides contained in the exhaust gas. There is concern that the characteristics may deteriorate. Therefore, it is preferable to use V in combination with a transition element such as Cu, Co, or Mn as the component (b). Thus, when V is added to the component (b), the initial catalyst characteristics (reduction characteristics of NOx) are somewhat deteriorated, but stable NOx reduction characteristics for a long period of time can be obtained.

As the first catalyst, in addition to the above-mentioned components (a) and (b), (c) rare earth elements (Ce, La, Nd, Sm, etc.)
You may use what added 1 type or 2 types or more of these.
(c) Addition of a rare earth element further improves the removal effect.

When a catalyst consisting only of (a) and (b) is used as the first catalyst, the compounding ratio is such that (a) is 10 to 90% and (b) is the weight ratio of the respective metal components. 10-90%
And preferably (a) is 25 to 75% and (b) is 25 to 75%.
75%. When (c) is also included, (a) is 10
-80%, (b) 10-80%, (c) 50% or less, preferably (a) 25-50%, (b) 25-50%,
(c) is 25 to 50%.

When a transition element such as Cu, Co, or Mn is used in combination with the V element as the component (b), other than the V element,
The weight ratio of the component (b) to the V element is 5/1 to 1/1
It is good to set it to about 5.

The first catalyst is supported on the exhaust gas inlet side of the molded body by the method described later.

In the present invention, in addition to the above-mentioned first catalyst, a second catalyst containing a platinum group element having high oxidizing ability is used. The second catalyst containing this platinum group element is the residual hydrocarbons and CO
Acts as a catalyst for purification of etc. The second catalyst may be a Pt-based catalyst or a Pd-based catalyst, a Pt-based and Pd-based mixed catalyst, or a Pt-based, Pd-based and Rh-based mixed catalyst. Further, in addition to the above platinum group-based catalyst, Au and / or Ag may be further contained. As described above, when Au and / or Ag is further added to the catalyst containing the platinum group element, HC
Purification characteristics such as CO and CO can be improved.

The second catalyst is supported on the exhaust gas outlet side of the molded body.

As described above, in the present invention, the above-mentioned first catalyst is loaded on the exhaust gas inflow side of the molded body, and the second catalyst is loaded on the exit side. As described above, when the two systems of catalysts are carried on the molded body, purification of exhaust gas becomes extremely good. That is, on the first catalyst on the inlet side, first, NOx is generated by HC.
Is reduced. Since the first catalyst is mainly composed of the base metal as described above, the production of SO ₃ can be suppressed.

Next, HC, CO, etc. remaining in the exhaust gas are oxidized on the second catalyst on the outlet side. Further, when the oxygen concentration decreases, NOx remaining on the second catalyst without being reduced on the first catalyst on the inlet side is reduced by CO and HC.

The above-mentioned first catalyst and second catalyst are
Although it may be directly supported on the molded body made of the above-mentioned ceramic material, it is preferable that a porous ceramic layer is further formed on the surface of the molded body and the catalyst is supported on the porous ceramic layer. .. When a porous ceramic layer having a surface area larger than that of the molded body is provided on the molded body and the catalyst is supported on the molded body, the contact area between the exhaust gas and the exhaust gas purifying material is increased, and the exhaust gas purifying ability is further improved. The specific surface area of the porous ceramic layer serving as the catalyst supporting layer is preferably 30 m ² / g or more.

As a material for forming the porous ceramic layer provided on the molded body, porous materials such as alumina, titania, zirconia, magnesia, titania-alumina, titania-silica, titania-zirconia, alumina-zirconia, and alumina-silica are used. Examples include ceramics of high quality and large surface area. In order to improve the NOx removal rate by hydrocarbons, it is particularly preferable to use the above-mentioned alumina-based ceramics, zirconia, titania, titania-zirconia, or the like. In addition, it is preferable to form the porous ceramic layer by a wash coat method or a sol-gel method described later so that the pressure loss due to the purifying material is not excessively increased.

When a porous ceramic layer is provided on the ceramic molded body and the first and second catalysts are carried on this, a porous ceramic layer of 3 to 15% by weight based on the ceramic molded body is provided. It is preferable to provide a catalyst for the porous ceramic layer. When the porous ceramic layer is less than the above lower limit value, it becomes difficult to support a sufficient amount of catalyst. Further, when the amount of the porous ceramic layer exceeds the above upper limit value, the pressure loss in the purification material becomes too large. More preferably, the porous ceramic layer is 5 to 12% by weight of the molded body.

The amount of the catalyst supported on the porous ceramic layer is 0.01 to 0.01% by weight of the first catalyst on the porous ceramic layer.
10% by weight, preferably 0.05 to 5% by weight, and 0.01 to 0.5% by weight of the second catalyst (both are converted to the metal content of the catalyst). More preferably, the supported amount of the first catalyst is 0.1 to 2% by weight with respect to the porous ceramic layer,
The amount of the second catalyst is 0.01 to 0.02% by weight. If the loading amount of the first catalyst is less than 0.01% by weight, the NOx purification rate will not be improved. Further, when the amount of the first catalyst that exceeds 10% by weight is carried, the reaction between HC and NOx is rather suppressed. On the other hand, the loading amount of the second catalyst is 0.01
If it is less than wt%, the purification performance of CO, HC, etc. remaining in the exhaust gas is not improved. Further, even if the amount of the second catalyst carried exceeds 0.5% by weight, the ability to purify CO, HC and the like is not significantly improved.

When the above-mentioned first and second catalysts are supported on the ceramic molded body without providing the porous ceramic layer or when the pellets are used as the carrier, the amount of the catalyst with respect to the exhaust gas is the same as the above range. Set the level so that

In the present invention, when a foam type molded body is used, the exhaust gas inlet side of the molded body has a low density, and the outlet side has a high density thin layer portion, and the first catalyst which is a catalyst for NOx reduction is used. HC remaining on the low-density portion of the compact
A second platinum group-based catalyst that functions as a catalyst for purifying CO or CO may be supported on the high-density thin layer portion on the exhaust gas outlet side of the molded body. In this way, since the inlet side of the molded body has a low density, the exhaust gas easily enters the pores in the molded body, and the exhaust gas receives an appropriate resistance due to the thin layer portion on the outlet side. It is possible to efficiently purify CO and HC in the portion and reduce NOx.

There are several possible methods for forming the high-density thin layer portion of the molded body on the exhaust gas outlet side. (A) A release agent composed of glycerin, water, and a surfactant on the bottom surface of the mold having a desired shape. A method in which a slurry such as cordierite is poured into this mold, the mold is separated, dried and then baked,
(b) A method in which a uniform molded body is first formed, and an organic binder and powders of cordierite or the like are mixed, and the mixture is applied to one surface of the molded body, dried, and baked are preferable.

The heat-resistant porous molded article thus formed has a porosity of about 60 to 90% and a pore size of 3 to 1000 μm (average of about 200 to 800 μm) in the low density portion, and has a high density and thinness. The layer portion preferably has a porosity of 40 to 70% and a pore size of about 3 to 400 μm (average about 20 to 300 μm). The thickness of the high density thin layer portion itself is preferably 5 to 2000 mm, more preferably 10 to 50 mm.

The size of the whole foam-type molded product can be variously changed according to the purpose, but in general, the molded product preferably has a diameter of 50 to 400 mm and a thickness of 5 to 30 mm. If necessary, a plurality of molded bodies may be laminated.

In addition to the above-described foam type molded body, a known honeycomb type molded body developed for exhaust gas purification for a gasoline engine or a diesel engine is used as a molded body as a base material for an exhaust gas purifying material. be able to.

The above-mentioned two types of catalysts can be loaded on the heat resistant porous molded body by the following method.

First, the method of holding the first catalyst on the exhaust gas inflow side of the molded body is carried out by an aqueous solution of metal carbonate, nitrate, acetate, chloride, hydroxide or the like which forms the first catalyst. For example, a method of immersing a honeycomb-type or foam-type heat-resistant porous molded body can be adopted. Further, a method of immersing the molded body in a solution of a compound containing a plurality of base metal-based metals such as alkali ferrocyanide to impregnate the catalyst is also possible.

For loading V, a solution of NH ₄ VO ₃ and oxalic acid can be used. Alternatively, an alkali vanadate (for example, potassium vanadate, sodium vanadate, and cesium vanadate) can be used to simultaneously support the alkali metal element and the V element.

The loading of the second catalyst on the portion of the exhaust gas which is on the outlet side can be carried out by immersing only the portion of the molded body on the exhaust gas outlet side in an aqueous solution of a chloride of a platinum group element or the like.

In order to increase the supported area of the catalyst, it is preferable to indirectly support the catalyst on the heat-resistant molded body through a carrier layer such as a porous ceramic having a large surface area, as described above. In order to make the pressure loss due to the purifying material moderate and to carry the catalyst uniformly, it is necessary to form a porous ceramic layer (support layer) on the surface of the molded body by using a wash coat method or a sol-gel method. Is good.

The wash coating method is a method of forming a ceramic layer serving as a catalyst carrier layer on the surface of a molded body by immersing the molded body in the above-mentioned ceramic slurry and drying it.

When this method is used, the catalytically active species can be supported by the impregnation method or the like after the formation of the ceramic layer to be the carrier layer. However, the washcoat method is carried out by using the ceramic powder pre-impregnated with the catalyst. For example,
The carrier layer supporting the catalyst can be formed by a single treatment.

There are two sol-gel methods, as described in detail below. The first method is to hydrolyze an organic salt (for example, an alkoxide) of a metal forming the ceramics for the catalytically active species carrier layer, coat the obtained sol on a honeycomb-type or foam-type molded body, and mix it with water vapor or the like. In this method, a ceramic film is formed by contact, followed by drying and firing, and finally carrying a catalytically active species. For example, when titania (TiO ₂ ) is used as the ceramics for the carrier layer and catalytically active species are supported on the titania, first, an alcohol solution of Ti alkoxide (for example, Ti (O-isoC ₃ H ₇ ) ₄ ) is added with CH ₃ A coating solution containing an acid such as COOH, HNO ₃ and HCl is produced. The molded body is dipped in this coating solution, pulled up, and then reacted with water vapor or water to cause gelation.

Next, when the honeycomb or foam type molded body is dried and fired, a titania layer is formed on the surface of the pores.

After the porous ceramic layer is formed by the above method, it is then impregnated with an aqueous solution of a carbonate, a nitrate, an acetate, a hydroxide, a chloride or the like of catalytically active species, and dried and fired again. The catalyst is supported.

The second method is a method of simultaneously coating the ceramics for the carrier layer and the catalytically active species on the honeycomb or foam type molded body. For example, first, an aqueous solution of an acid such as CH ₃ COOH, HNO ₃ , and HCl and a salt of a catalytically active metal species is added to an alcohol solution of Ti alkoxide to form a coating solution. Then, after immersing the molded body in the coating liquid, it is reacted with water vapor or water to form a sol,
Furthermore, gelation is performed. Then, the molded body is dried and fired to form a coating layer made of titania carrying a catalyst.

In any of the above sol-gel methods,
As the salt of the catalytically active metal species, any kind of salt such as carbonate, nitrate, acetate and hydroxide can be used as long as it is soluble in water. In addition, it is preferable to add a dispersant such as ethylene glycol for the purpose of uniformly dispersing the salt of the catalyst metal in the alcohol solution of the alkoxide.

Although the acid is added as a catalyst for the hydrolysis reaction during gelation, the hydrolysis reaction can be promoted by adding an alkali instead of the acid.

Although titania has been described as an example of the ceramics for the carrier layer in the above, other ceramics can be similarly loaded by the sol-gel method. For example, when a catalytically active species is supported on alumina, an alkoxide of Al is used and the same method as in the case of titania described above is performed. The same applies when other porous carriers are used.

According to the sol-gel method, it is possible to support the catalyst in the molded body extremely uniformly, and it becomes easy to support the catalyst even in a high density region.

Platinum group elements, Au and / or
Alternatively, as a method of supporting Ag, Pt, Pd, Rh is added to a carrier layer formed by a washcoat method or a sol-gel method.
A method of impregnating with an aqueous solution of a chloride of a platinum group element such as the above, an aqueous solution of a chloride of Au and / or Ag, and drying and firing can be applied.

Each metal component in the first catalyst exists as an oxide in the carrier layer. Further, each metal component in the second catalyst exists in the carrier layer in the elemental state or the oxide state.

The exhaust gas containing almost no particulate carbon material (particulate) in the present invention means an exhaust gas containing 0.003 g / Hp · hour or less of particulate carbon material. Exhaust gas having such a concentration of the particulate carbon material is found in exhaust gas from a gasoline engine or the like. Exhaust gas from a diesel engine usually contains about 0.3 to 0.6 g / Hp · hour of particulate carbon material, although it varies depending on engine operating conditions, load, and the like.

Exhaust gas from a gasoline engine or the like containing almost no particulate carbonaceous material (particulates) usually contains 100 to 500 unburned hydrocarbons (HC) in an oxidizing atmosphere.
Approximately ppm, NOx is contained in the range of 200-4000ppm. Also,
The oxidizing atmosphere in the present invention refers to an atmosphere containing more oxygen than the theoretical amount of oxygen required for burning unburned components such as carbon monoxide and hydrocarbons. Usually, oxygen content is 4% by volume
The above exhaust gas has an oxidizing atmosphere. Examples of HC include propane, propylene, acetylene, ethylene and the like, but generally the reactivity is higher in the order of triple bond (acetylene etc.)> Double bond (ethylene, propylene etc.)> Single bond (propane). Usually, HC in exhaust gas is mainly composed of methane, ethylene and acetylene, so the NOx reduction reaction temperature is 200 to 500 ° C, preferably 250 to 450 ° C.
If the reaction temperature is too high, combustion of HC itself occurs, and the NOx removal rate is not improved. When the amount of HC acting as a reducing agent is small in the exhaust gas, the amount of HC such as propane and propylene necessary for reducing NOx can be forcibly introduced.

The present invention will be described in more detail with reference to the following specific examples. Example 1 Cordierite foam-type molding (disc-shaped with a thickness of 50 m
m, apparent volume 35 cm ³ , weight 12 g, porosity 85%),
Γ-Al ₂ O ₃ was coated on the molded body by 10% (weight%, the same applies hereinafter) by the above-mentioned wash coating method. A portion other than one end portion of the obtained molded body was impregnated with CuCl _{2 in} an aqueous solution of 10% with respect to γ-Al ₂ O ₃ (the metal content was the same below), and Ce (NO _{3) 3} aqueous solution was impregnated with Ce 2.5% with and then with K ₂ CO ₃ aqueous solution and impregnated with K 2.5%.

On the other hand, for the above-mentioned end portion not impregnated,
0.02% of Pt was impregnated in γ-Al ₂ O ₃ using an aqueous solution of H ₂ PtCl ₆ .

After drying the above-mentioned impregnated molded body, 500
It was calcined at ℃ for 3 hours and used as an exhaust gas purifying material.

With this purification material, with the K / Cu / Ce catalyst as the inlet side, O ₂ 10%, NO 800 ppm, CO 500 ppm,
C ₃ H ₆ 300ppm, using a reaction gas which becomes N ₂ at the balance with 10% water content, at 300 ° C, the flow rate of the reaction gas was 5.8 liters / minute, and the purification rates of NO, CO and C ₃ H ₆ were I asked. The results are shown in Table 1.

Example 2 Cordierite honeycomb type molded body (disc-shaped, thickness 50
mm, apparent volume 35 cm ³ , weight 17 g, porosity 74%)
Then, 10% of TiO ₂ was coated on the molded body by the above-mentioned wash coating method.

An aqueous solution of CuCl ₂ was used to apply 10% of Cu to TiO ₂ except for one end of the obtained molded body.
Impregnated with 2.5% La using an aqueous solution of La (NO ₃ ) _3.
Impregnation, then 2.5% of Cs was impregnated with an aqueous solution of CsNO ₃ .

On the other hand, at the end portion not subjected to the above impregnation, H ₂
0.02% of Pt was impregnated with respect to TiO ₂ using an aqueous solution of PtCl ₆ .

After the above impregnation, the molded body is dried and
It was fired at 500 ° C. for 3 hours to obtain an exhaust gas purification material.

With this purification material, with the Cs / Cu / La catalyst as the inlet side, O ₂ 10%, NO 800 ppm, CO 500 ppm, C
₃ H ₈ 300 ppm, water content 10%, the balance is a reaction gas that is substantially N ₂ gas, the reaction gas flow rate is 5.8 liters / minute at 300 ℃, NO, CO, C ₃ H ₈ purification rate I asked.
The results are shown in Table 1.

Example 3 Foam type molded body made of cordierite (disk-shaped with a thickness of 50 m
m, apparent volume 35 cm ³ , weight 12 g, porosity 85%),
By the washcoat method described above, 10% of γ-Al ₂ O ₃ was coated on the molded body. Γ-Al ₂ O was prepared by using an aqueous solution of CuCl _{2 in} a portion other than one end of the obtained molded body.
Cu was impregnated with 0.5% of ₃ (the same applies to the metal content below), 0.2% of Ce was impregnated with Ce (NO ₃ ) ₃ aqueous solution, and then 0.2% of Cs was impregnated with CsNO ₃ aqueous solution. did.

On the other hand, for the end portion not subjected to the above-mentioned impregnation,
0.02% of Pt was impregnated in γ-Al ₂ O ₃ using an aqueous solution of H ₂ PtCl ₆ .

After drying the above-mentioned impregnated molded body, 500
It was calcined at ℃ for 3 hours and used as an exhaust gas purifying material.

Regarding this purification material, with the Cs / Cu / Ce catalyst as the inlet side, O ₂ 10%, NO 800 ppm, CO 500 ppm,
C ₃ H ₆ 300ppm, using a reaction gas which becomes N ₂ at the balance with 10% water content, at 300 ° C, the flow rate of the reaction gas was 5.8 liters / minute, and the purification rates of NO, CO and C ₃ H ₆ were I asked. The results are shown in Table 1.

Example 4 A honeycomb type molded body made of cordierite (having a disc shape and a thickness of 50)
mm, apparent volume 35 cm ³ , weight 17 g, porosity 74%)
Then, 10% of TiO ₂ was coated on the molded body by the above-mentioned wash coating method.

An aqueous solution of CuCl ₂ was used to apply Cu of 0.5% to TiO ₂ to a portion other than one end of the obtained molded body.
Impregnated with 0.2% La using an aqueous solution of La (NO ₃ ) _3.
It was impregnated and then 0.2% of Cs was impregnated with an aqueous solution of CsNO ₃ .

On the other hand, at the end portion not subjected to the above-mentioned impregnation, H ₂
0.02% of Pt was impregnated with respect to TiO ₂ using an aqueous solution of PtCl ₆ .

After the above impregnation, the molded body is dried, and
It was fired at 500 ° C. for 3 hours to obtain an exhaust gas purification material.

Regarding this purification material, with the Cs / Cu / La catalyst as the inlet side, O ₂ 10%, NO 800 ppm, CO 500 ppm, C
₃ H ₈ 300 ppm, water content 10%, the balance is a reaction gas that is substantially N ₂ gas, the reaction gas flow rate is 5.8 liters / minute at 300 ℃, NO, CO, C ₃ H ₈ purification rate I asked.
The results are shown in Table 1.

Comparative Example 1 In the same manner as in Example 3, a cordierite foam-type molding was coated with 10% of γ-Al ₂ O ₃ by a wash coating method, and Cu chloride was added thereto. Cu was impregnated in 10% of γ-Al ₂ O ₃ using the aqueous solution of. Regarding the purification material obtained above, NO, CO under the same conditions as in Example 4
And the purification rates of C ₃ H ₈ were obtained. The results are shown in Table 1.

Comparative Example 2 In the same manner as in Example 3, a cordierite foam-type molded product was coated with 10% of γ-Al ₂ O _3, and an aqueous solution of Pt chloride was used to form γ-Al ₂ O. Impregnated with 0.2% Pt for ₃ %. With respect to the purification material obtained above, the purification rates of NO, CO and C ₃ H ₈ were obtained under the same conditions as in Example 4. The results are shown in Table 1.

Table 1 Example No. Purification rate (%) NO CO HC Example 1 20 60 50 Example 2 25 60 50 Example 3 40 60 50 Example 4 32 60 50 Comparative Example 1 0 0 5 Comparative Example 2 0 90 70

As can be seen from Table 1, in the purification materials of Examples, the NO purification rate is 20% or more. In particular, an example in which the amount of the component carried in the first catalyst is reduced (Examples 3 and 4)
The NO purification rate was over 30%. On the other hand, the purification material of the comparative example does not substantially purify NO. Further, it can be seen that the purifying materials of the examples also have a considerable purifying effect on CO and HC.

Examples 5 to 7 Foam type moldings made of cordierite (apparent volume 35 cm
³ , weight 17 g, porosity 74%), and ZrO ₂ (Example 5), TiO ₂ —ZrO ₂ by the above washcoat method.
(Example 6) or the alumina-based oxide (Example 7) was coated on the molded body by 10%.

ZrO ₂ layer, TiO ₂ —ZrO ₂ layer obtained above,
Alternatively, in each of the Examples, the following eight first catalyst species were loaded on the Al ₂ O ₃ layer in the same manner as in Example 2.
The amount of each metal loaded is 0.2% by weight of the alkali metal element, 0.5% by weight of the transition metal element, and when the rare earth element is also loaded, the amount of the rare earth element loaded on the catalyst loading layer. The supported amount was 0.2% by weight.

A second catalyst was loaded on the end of the molded body on which the first catalyst was not loaded, in the same manner as in Example 2.

First catalyst species (1) Cs / Cu (2) Cs / Co (3) Cs / Mn (4) Cs / V (5) Cs / Co / La (6) Cs / Co / Ce (7 ) Cs / Mn / Ce (8) Cs / Mn / La

For each of the obtained purification materials, the purification rates of NO, CO and C ₃ H ₈ were obtained in the same manner as in Example 2.
Purification rates similar to those in Example 2 were obtained.

Example 8 A cordierite foam molding similar to that used in Example 3 was subjected to γ by the washcoat method described above.
-Al ₂ O ₃ was coated on the molded body by 10%. A part of the obtained molded body other than one end is impregnated with 0.5% Cu in γ-Al ₂ O ₃ using an aqueous solution of CuCl ₂ and a mixed solution of an NH ₄ VO ₃ aqueous solution and oxalic acid. And V is 0.
It is impregnated with 5% and Ce (NO ₃ ) ₃ solution is used to add 0.2% Ce.
% Cs, and then 0.2% Cs was impregnated with an aqueous CsNO ₃ solution.

On the other hand, for the end portion not subjected to the above-mentioned impregnation,
0.02% of Pt was impregnated in γ-Al ₂ O ₃ using an aqueous solution of H ₂ PtCl ₆ .

After the molded body impregnated with the above is dried, 500
It was calcined at ℃ for 3 hours and used as an exhaust gas purifying material.

With respect to this purification material, NO, CO and C were obtained under the same conditions as in Example 3 with the Cs / Cu / V / Ce catalyst as the inlet side.
The purification rate of ₃ H ₆ was determined. The results are shown in Table 2.

Further, when the purification rates of NO, CO and C ₃ H ₆ were obtained 10 hours after the passage of the above gas, the purification rates were almost the same as the results of Example 8 shown in Table 2. It was

Example 9 The same cordierite honeycomb molded body as that used in Example 4 was added with TiO 2 by the above-mentioned wash coating method.
10% of ₂ was coated on the molded body.

Cu was added to the TiO ₂ layer at a portion other than one end of the obtained molded body by using an aqueous solution of CuCl _{2 in} an amount of 0.5.
%, Impregnated with 0.5% V using a mixed solution of NH ₄ VO ₃ aqueous solution and oxalic acid, and 0.2% La with an aqueous solution of La (NO ₃ ) ₃ and then an aqueous solution of CsNO ₃ . Was used to impregnate 0.2% of Cs.

On the other hand, at the end portion not subjected to the above impregnation, H ₂
0.02% of Pt was impregnated in TiO ₂ using an aqueous solution of PtCl ₆ .

After the above impregnation, the molded body is dried, and
It was fired at 500 ° C for 3 hours to obtain an exhaust gas purifying material.

With respect to this purification material, the purification rates of NO, CO and C ₃ H ₈ were obtained under the same conditions as in Example 4. The results are shown in Table 2.

Further, when the purification rates of NO, CO and C ₃ H ₈ were obtained 10 hours after the passage of the above gas, the purification rates were almost the same as the results of Example 9 shown in Table 2. It was

[0095]

As can be seen from Table 2, in the purification materials of Examples, the NO purification rate is about 30%. In addition, as described above, the purification characteristics in Examples 8 and 9 are excellent in exhaust gas purification even after the passage of 10 hours from the start of exhaust gas passage, and excellent durability. Further, it can be seen that the purifying materials of the examples also have a considerable purifying effect on CO and HC.

Examples 10 to 12 A molded article similar to the cordierite foam-molded article used in Example 3 was applied to the above-mentioned wash-coating method.
10% ZrO ₂ (Example 10), TiO ₂ − based on the molded body
ZrO ₂ (Example 11) or alumina-based oxide (Example 1)
A catalyst carrier layer consisting of 2) was formed.

In the same manner as in Example 8, the following seven types of first catalyst species were loaded on the catalyst support layer, and the catalyst loading layer (ZrO ₂ , Ti
O ₂ -ZrO ₂ or alumina-based oxide) Pt 0.02
%, A purifying material was prepared. The amount of each metal supported on the first catalyst is 0.2% by weight of an alkali metal element, 0.5% by weight of a transition metal element, and a rare earth element on the catalyst carrier layer. In addition, the supported amount was 0.2% by weight.

Catalytic species (1) Cs / V / Cu (2) Cs / V / Co (3) Cs / V / Mn (4) Cs / V / Co / La (5) Cs / V / Co / Ce ( 6) Cs / V / Mn / Ce (7) Cs / V / Mn / La

With respect to the obtained purification material, the purification rates of NO, CO and C ₃ H ₈ were obtained in the same manner as in Example 9. As a result, the same purification rate as in Example 9 was obtained.

[0101]

As described above in detail, by using the exhaust gas purifying material of the present invention, NOx in exhaust gas can be efficiently purified under a relatively low temperature condition of about 300 ° C. even in an oxidizing atmosphere. be able to.

The purification method of the present invention is suitable for purification of an exhaust gas such as an exhaust gas of a gasoline engine, which hardly contains particulate carbonaceous substances.

Claims (5)

[Claims] 1. A purifying material for exhaust gas which contains almost no particulate carbon material and becomes an oxidizing atmosphere, wherein one kind of (a) an alkali metal element is present in the inlet side portion of the heat resistant porous molded body. Or two or more kinds, and (b) Group IB and IIB of the periodic table
V excluding group A, group VA, group VIA, group VIIA, and platinum group
1 selected from the group consisting of Group III transition metals and Sn
One or two or more elements and (c) one or more rare earth elements are supported on the first catalyst, and one or two elements are provided on the outlet side of the molded body. An exhaust gas purifying material, characterized in that a second catalyst comprising the above platinum group element is supported, and the second catalyst is supported by a photochemical method. 2. The exhaust gas purifying material according to claim 1, wherein the second catalyst on the outlet side portion of the molded body further contains Au and / or Ag. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the two catalysts are carried on a carrier layer provided on the surface of the molded body. 4. The exhaust gas purifying material according to claim 3, wherein the carrier layer is formed by a wash coat method or a sol-gel method. 5. A method for purifying an exhaust gas which contains almost no particulate carbon material and which is in an oxidizing atmosphere, using the exhaust gas purifying material according to any one of claims 1 to 4.
A method for purifying exhaust gas, which comprises reducing unoxidized hydrocarbons present in the exhaust gas as a reducing agent to reduce nitrogen oxides in the exhaust gas.