JPH0952051A - Exhaust gas purification catalyst and exhaust gas purification method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To effectively remove nitrogen oxides from exhaust gas in an oxygen-excess atmosphere regardless of the kind of hydrocarbon as a reducing agent, and a catalyst having excellent durability even at high temperature. And a method of purifying exhaust gas. A carrier made of silicon carbide is selected from the group consisting of (a) iridium, (b) at least one element selected from the titanium group, and (c) an alkali metal and an alkaline earth metal. An exhaust gas purification catalyst containing at least one element, and an exhaust gas purification method using the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exhaust gas discharged from various internal combustion engines, boilers, gas turbines, etc., particularly nitrogen oxides (NO) in exhaust gas in which excess oxygen coexists.
The present invention relates to an exhaust gas purification catalyst capable of effectively removing x) and an exhaust gas purification method.

[0002]

2. Description of the Related Art NOx emitted from various internal combustion engines
Causes photochemical smog and acid rain, and its removal from the source is an urgent issue. In recent years, in order to prevent global warming, it has been required to suppress the emission of carbon dioxide (CO ₂ ), and the air-fuel ratio (A / F = 14.
Attention is paid to a lean burn engine that suppresses gasoline consumption (that is, CO ₂ emission) by burning gasoline with an air-fuel ratio larger than 6). Further, the lean combustion method is being adopted also in gas engines and gas turbines, and also in diesel engines and boilers, etc., where lean combustion is also performed, and removal of NOx is also required in these cases.

A conventional three-way catalyst (TWC) method has been used for treating automobile exhaust gas, but this method is used for treating NOx in exhaust gas in which oxygen is in excess of the stoichiometric ratio as described above. Since the method is not effective, as a catalyst for removing NOx in the exhaust gas in the coexistence of excess oxygen, a copper ion exchange zeolite catalyst (for example, JP 63-100919 A), a noble metal ion exchange zeolite catalyst (for example, JP No. 1-135541) and a noble metal-supported porous metal oxide catalyst (for example, Japanese Patent Laid-Open No. 3-221144).

However, the above exhaust gas purifying catalysts and purifying methods have the following problems, respectively, and are not practical. That is, the copper ion exchange zeolite catalyst and the noble metal ion exchange zeolite catalyst
At a high temperature of 50 to 700 ° C., irreversible deactivation occurred within a few hours due to water vapor contained in the exhaust gas, and it was not practical.

The noble metal-supported porous metal oxide catalyst is also used as a hydrocarbon (HC) (herein, as a reducing agent for NOx due to the strong catalytic activity of the noble metal).
The term "hydrocarbon" means not only a hydrocarbon in a narrow sense but also an oxygen-containing hydrocarbon which is a partial oxide thereof, such as alcohols, ketones, etc.) However, there is a problem in that the selectivity of the NOx reduction reaction cannot be enhanced.

On the other hand, a catalyst in which iridium and an alkali metal are supported on a refractory inorganic oxide carrier such as alumina has already been known (Japanese Patent Publication No. 56-54173), but recently, the present applicant has proposed that a metal carbide And a catalyst comprising iridium supported on a carrier comprising at least one selected from metal nitrides (JP-A-6-31173), and a catalyst comprising iridium and an alkaline earth metal (JP-A-7- No. 31884) discloses that NOx selective reduction performance is relatively high even in the presence of excess oxygen.

However, regarding such a catalyst in which iridium or iridium and an alkaline earth metal are supported on a metal carbide or a metal nitride, or a catalyst in which iridium and an alkali metal are supported on a refractory inorganic oxide carrier such as alumina. However, since the NOx removing ability is highly dependent on the oxygen and hydrocarbon concentrations, NOx is not always sufficiently sufficient under conditions where the oxygen concentration in the exhaust gas is high or conditions where the hydrocarbon concentration of the reducing agent is low. Sometimes it could not be removed.

Further, depending on the engine specifications such as diesel engine, HC contained in exhaust gas is NOx.
In comparison with the amount of HC required for the selective reduction of [THC (C
Even if it is necessary to add a reducing agent, it is desirable to reduce the amount of HC to be added in terms of fuel consumption. It has been desired to develop a catalyst exhibiting excellent performance and excellent durability.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional catalysts for treating exhaust gas as described above, and an object thereof is to provide a reducing component containing a hydrocarbon. With respect to exhaust gas containing oxygen and nitrogen oxide in excess of the stoichiometric amount required to oxidize the reducing component and the reducing component, a high nitrogen oxide removal rate can be obtained, and further in the presence of water and SOx. It is an object of the present invention to provide an exhaust gas purifying catalyst having high temperature durability and an exhaust gas purifying method using the same.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted research to solve the above problems and achieve the above objects, and as a result, (a) iridium and (a) iridium were added to a carrier made of silicon carbide.
The object is achieved by an exhaust gas purification catalyst containing (b) at least one element selected from the titanium group and (c) at least one element selected from the group consisting of alkali metals and alkaline earth metals. The present invention has been completed by finding that it can be obtained.

That is, according to the present invention, a carrier made of silicon carbide comprises (a) iridium, (b) at least one element selected from the titanium group, and (c) an alkali metal and an alkaline earth metal. An exhaust gas purifying catalyst containing at least one element selected from the group and an exhaust gas purifying method using the same.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention will be described in detail below. The exhaust gas purifying catalyst of the present invention (hereinafter referred to as "catalyst") is a carrier of silicon carbide,
Prepared by supporting (a) iridium, (b) at least one element selected from the titanium group, and (c) at least one element selected from the group consisting of alkali metals and alkaline earth metals. (Hereinafter, the elements (a) to (c) may be collectively referred to as “catalyst element”).

The silicon carbide used as a carrier for the catalytic element in the present invention preferably has a low specific surface area and is non-porous, and specifically it is 35 m ² / g or less (more preferably 0.1 to 30 m ^2). / G) BET specific surface area and 1.0c
m ³ / g or less (more preferably 0.1 to 0.8 cm ³ / g)
It is preferable that it has a pore volume of.

On the other hand, among the catalytic elements, examples of the element selected from the titanium group (b) include zirconium and titanium, and the element selected from the alkali metal and alkaline earth metal (c). Examples of include potassium, sodium, lithium, magnesium, calcium, strontium, barium, and the like.

The presence state of the supported catalyst element is not particularly limited, and examples of the presence state include a metallic state,
Examples thereof include an oxide state, an alloy state, a complex oxide state, and a state in which these states are mixed.

Of the catalytic elements, the amount of iridium supported on the carrier is calculated as metallic iridium based on the weight of the catalyst.
The amount is preferably 0.05 to 10.0% by weight, more preferably 0.1 to 5.0% by weight. The amount of at least one element selected from the group consisting of titanium group loaded on the carrier is preferably 0.1 to 40 times, more preferably 0.5 to 20 times the atomic ratio of iridium. Double.

Further, the amount of at least one element selected from the group consisting of alkali metals and alkaline earth metals carried on the carrier is preferably 0.1 to 40 times the atomic ratio of iridium, It is more preferably 0.5 to 20 times.

The method of preparing the catalyst of the present invention is not particularly limited, and conventionally known methods such as evaporation / drying, spray drying, water absorption and impregnation can be applied.

The following method can be exemplified as a specific catalyst preparation method. (I) Iridium (hereinafter sometimes referred to as "catalyst element (a)") and at least one element selected from the titanium group (hereinafter sometimes referred to as "catalyst element (b)")
And a mixed solution (or suspension) of each raw material salt of at least one element selected from the group consisting of alkali metals and alkaline earth metals (hereinafter sometimes referred to as “catalyst element (c)”) Is added to the silicon carbide carrier to evaporate
Simultaneous loading method of baking after drying. (Ii) First, a solution of a raw material salt of the catalyst element (a) is added to the silicon carbide carrier, evaporated and dried to dryness, and then calcined to immobilize the catalyst element (a) as an insoluble compound or metal on the carrier. , The catalytic element (b) and the catalytic element (c) are sequentially supported and immobilized in the same manner as the catalytic element (a), and as a result, the catalytic element (a), the catalytic element (b) and the catalytic element A sequential loading method of loading (c). (Iii) Contrary to (ii), a sequential loading method in which the catalyst element (c) is first supported and immobilized on the silicon carbide carrier, and then the catalyst (b) and the catalyst (c) are sequentially supported and immobilized.

Catalytic elements in the preparation of the catalyst of the present invention
(A), catalyst element (b), and starting source of catalyst element (c)
There are no particular restrictions on fees. Release of catalytic element (a)
Examples of the raw material include iridium trichloride (IrCl)
_Three), Iridium chloride (H₂IrCl₆), Iriji chloride
Sodium umate (Na_ThreeIrCl₆), The same (Na₂Ir
Cl₆), Iridium nitrate [Ir (NO_Three)_Four ], Sulfate
Rhidium [Ir (SO_Four)₂ ] Water-soluble salts of iridium such as
Is used. Also, Ir_Three(CO)₁₂Iridium etc.
Metal carbonyl of IrCl (CO) (PPh_Three)₂Etc.
Organometallic complexes of iridium are mixed with hexane, acetone, and chlorine.
Even when dissolved in an organic solvent such as loform or ethanol
good.

On the other hand, as the starting salt of zirconium among the catalytic elements (b), for example, zirconium chloride oxide octahydrate (ZrCl ₂ O.8H ₂ O), zirconium tetrachloride (ZrCl ₄ ), zirconium nitrate dihydrate. Hydrate [ZrO
_{(N0 3) 2 · 2H 2} O ], zirconium oxide (Zr
O ₂ ), zirconium silicate (ZrSiO ₄ ) and the like are used. Examples of the starting salt of titanium include titanium sulfate [Ti (SO ₄ ) ₂ ] solution, titanium chloride [TiCl ₄ ),
Titanium oxide (TiO ₂ ) or the like is used.

Among the catalytic elements (c), alkali gold
As a starting material for potassium, which is one of the genus, for example,
Potassium chloride (KCl), potassium carbonate (K₂CO_Three),
Potassium nitrate (KNO_Three), Potassium acetate (CH_ThreeCOO
K), potassium sulfate (K₂SO_Four), Potassium hydroxide (K
OH) and the like are used. Similarly, one of alkaline earth metals
As a starting material for the seed magnesium, for example, salt
Magnesium chloride (MgCl₂), Basic magnesium carbonate
, Magnesium nitrate hexahydrate [Mg (NO_Three )₂・ 6H
₂O], magnesium acetate tetrahydrate [(CH_ThreeCOO)₂
Mg ・ 4H₂O], magnesium sulfate (MgSO 4_Four),water
Magnesium oxide [Mg (OH)₂] Etc. are used.
Departure of other alkali metals or alkaline earth metals
Chloride is used as a raw material as well as potassium and magnesium
Substances, carbonates, nitrates, acetates, sulfates, hydroxides, etc.
Used.

In the above-mentioned simultaneous carrier method or sequential carrier method, the atmosphere for firing and decomposing the iridium compound, titanium group compound, alkali metal and alkaline earth metal compound supported as a catalyst precursor on the carrier is Depending on the kind of the precursor, air, vacuum, a stream of an inert gas such as nitrogen, or a stream of hydrogen is appropriately selected. The firing temperature is preferably 300 to 1,000 ° C, more preferably 600 to 900 ° C. The firing time may be appropriately selected, but is usually about 5 minutes to 20 hours, preferably about 10 minutes to 5 hours. Further, the firing may be performed by combining a plurality of treatments stepwise. For example,
After firing in air at 600-800 ° C, 600-in nitrogen stream
You may process at 900 degreeC.

No particular limitation is imposed on the form of the catalyst of the present invention prepared as described above when used for exhaust gas purification.
For example, a form in which the catalyst is filled in a certain space, a form in which the catalyst is molded into a predetermined shape, and the like are included. When molding into a predetermined shape, the catalyst may be mixed with a suitable binder or molded without a binder.

When the catalyst takes a predetermined form, it is also possible to employ a method in which the carrier is preliminarily molded into an appropriate shape prior to supporting the active ingredient on the carrier. In this case, the molding shape is not particularly limited, and examples thereof include a spherical shape, a pellet shape, a cylindrical shape, a honeycomb shape, a spiral shape, a granular shape, and a ring shape. Further, the shape, size and the like can be arbitrarily selected according to usage conditions.

The catalyst of the present invention is preferably used by being coated on a refractory supporting substrate. Examples of the refractory support substrate include ceramics such as cordierite and mullite, and metals such as stainless steel integrally formed into a honeycomb shape or a foam.

As a method for coating the supporting substrate with the catalyst of the present invention, the catalyst may be coated (eg, washcoat) on the surface of the supporting substrate with or without an appropriate binder. Alternatively, the support substrate may be previously coated with only the carrier by the coating method as described above, and the active component may be supported on the support substrate coated with only the carrier.

The binder used for the above coating is
For example, an inorganic binder such as alumina sol, silica sol, titania sol can be used. The coating of the catalyst powder on the supporting substrate can be performed, for example, by adding alumina sol and water to the catalyst powder, kneading to form a slurry, and immersing the supporting substrate in the slurry, followed by drying and firing. .

The catalyst coating amount on the supporting substrate is not particularly limited, and preferably 10 to 200 per unit volume of the supporting substrate.
g / l, more preferably 50 to 150 g / l.
The amount of iridium supported per unit volume of the supporting substrate is preferably 0.005 to 20.0 g / l, more preferably 0.05 to 7.5 g / l in terms of metal. The amount of the catalytic element (b) supported on the carrier is preferably 0.1 to 40 times the atomic ratio of iridium, more preferably 0.1.
It is 5 to 20 times. Further, the amount of the catalytic element (c) supported on the carrier is preferably 0.1 in atomic ratio with respect to iridium.
It is 1 to 40 times, and more preferably 0.5 to 20 times.

Next, an exhaust gas purification method using the catalyst of the present invention will be described. The gas space velocity of the exhaust gas is not particularly limited, and preferably the space velocity is 5,000 to 200,0.
00 / hr, more preferably 10,000 to 150,000
It is 0 / hr. The catalyst inlet temperature of the exhaust gas for the selective reduction of NOx is preferably 100.
To 700 ° C, and more preferably 200 to 600 ° C.

In the exhaust gas which is the object of the exhaust gas purification method of the present invention, the weight ratio A / F of the oxidizing component and the reducing component is a stoichiometric amount (A / F = 14.6, O ₂ concentration =
0.5%), or exhaust gas on the reducing component-lean side (A / F> 14.6, O ₂ concentration> 0.5%). The latter exhaust gas is preferably purified.

[0032] That is, the catalyst of the present invention have excellent NOx removal performance in the vicinity of the stoichiometric amount, in the conventional noble metal catalysts oxygen showed only significantly poor NOx reduction selectivity Any excess atmosphere (O ₂ It is characterized in that it has an excellent NOx removal performance even at a concentration> 0.5%), and can treat such exhaust gas.

Therefore, according to the catalyst of the present invention, the oxygen concentration is 5 to 5 as in the exhaust gas of a gasoline Linburn engine.
In the 10% region, a sufficient NOx reducing ability can be obtained only by the HC in the exhaust gas without adding a reducing agent HC from the outside.

In the catalyst of the present invention, the HC contained in the exhaust gas, which is represented by the exhaust gas of a diesel engine using kerosene, light oil, heavy oil A, etc. as a fuel, is the HC necessary for the selective reduction of NOx. Shortage compared to stoichiometric amount (THC / N
Even if Ox <1) and a reducing agent needs to be added,
Excellent NOx with a small addition amount of THC / NOx = 5
It exerts a reducing ability.

[0035]

EXAMPLES The present invention will be described in more detail with reference to Examples and Test Examples, but the present invention is not limited to these Examples.

Example 1 Preparation of catalyst-coated honeycomb A-1: (1) Commercially available SiC powder (specific surface area: 15 m ² / g, pore volume: 0.54 cm ³ / g) in 96.2 g of deionized water 2. 0k
g was added and stirred for 20 minutes to obtain a SiC powder slurry. To this slurry, deionized water 160 g, zirconium oxychloride octahydrate corresponding to the metal zirconium 1.8g containing iridium chloride acid (H ₂ IrCl _6), which corresponds to iridium 1.2g (ZrCl ₂ O · 8H ₂ O)
160 g of a deionized aqueous solution containing 0.5 g of potassium metal.
After adding a mixed solution of 160 g of a deionized aqueous solution containing potassium chloride (KCl) corresponding to 8 g, the mixture was transferred onto a glass lined dish with a steam jacket, and the water was evaporated with stirring for 4 hours.

The obtained solid matter is dried by an electric drier 105
After drying at 16 ° C. for 16 hours, the product was crushed, the crushed product was placed in a quartz tray, and baked in an electric furnace at 750 ° C. for 30 minutes in air. The obtained fired powder is heated at 800 ° C in a 100% nitrogen stream.
After treatment for 1 hour with metal, 1.2 wt% Ir-1.8 wt% Zr-0.8 wt% K (Ir / Zr / K = 1 / 3.2
/3.3 (atomic ratio)) / SiC catalyst powder was obtained.

(2) 1 g of deionized water was added to 60 g of the above catalyst powder.
20 g and alumina sol (Al₂O_Three Solid content 10% by weight
Yes) 8.0g was added, and the resulting mixture was ball milled.
Wet grinding was carried out for 5 hours to obtain a catalyst slurry. This sla
From a commercially available 400 cell cordierite honeycomb
1 inch diameter and 2.5 inch long core pierce
After soaking the base, pull it up and remove excess slurry with an air blower.
Removed with rho. After that, the core piece with the catalyst attached
Is dried at 300 ° C for 20 minutes and then at 500 ° C for 30 minutes.
Fired for 1 minute and converted to dry per 1 liter of honeycomb volume
Ir-Zr-K / SiC catalyst coating coated with 100 g of
A honeycomb (A-1) was obtained.

Example 2 Preparation of Catalyst-Coated Honeycomb A-2: In the above Example 1 (1), SiC powder was changed to 90.2 g, iridium chlorochloride was converted to metal iridium in an amount of 1.2 g, and zirconium chloride oxide was converted to metal. Example 1 except that 5.4 g in terms of zirconium and 3.2 g in terms of metallic potassium were used instead of potassium chloride.
In the same manner as in (1), 1.2 wt% Ir-5.
4 wt% Zr-3.2 wt% K (Ir / Zr / K = 1 /
A powder of 9.5 / 13.1 (atomic ratio) / SiC catalyst was obtained.

The catalyst powder was wash-coated on a honeycomb by the same method as in Example 1 (2), and 100 g of dry-converted Ir-Z per liter of honeycomb volume was coated.
An r-K / SiC catalyst-coated honeycomb (A-2) was obtained.

Example 3 Preparation of Catalyst-Coated Honeycomb A-3: In Example 1 (1), SiC powder was changed to 96.6 g, iridium chlorochloride was converted into metallic iridium in 2.4 g, and zirconium oxide chloride octahydrate was used. 2.4 wt% Ir in terms of metal in the same manner as in Example 1 (1) except that the amount of the substance was changed to 0.6 g in terms of metallic zirconium and the amount of potassium chloride was changed to 0.4 g in terms of metallic potassium.
-0.6 wt% Zr-0.4 wt% K (Ir / Zr / K =
A powder of 1 / 0.5 / 0.8 (atomic ratio) / SiC catalyst was obtained.

The catalyst powder was wash-coated on the honeycomb in the same manner as in Example 1 (2), and 100 g of dry-converted Ir-Z per liter of honeycomb volume was coated.
An r-K / SiC catalyst-coated honeycomb (A-3) was obtained.

Example 4 Preparation of catalyst-coated honeycomb A-4: Example 1 (1) except that sodium chloride (NaCl) corresponding to 0.8 g of metallic sodium was used instead of potassium chloride. In the same manner as (1), 1.2 wt% I in terms of metal
r-1.8 wt% Zr-0.8 wt% Na (Ir / Zr /
Na = 1 / 3.2 / 5.6 (atomic ratio)) / SiC catalyst powder was obtained.

The catalyst powder was wash-coated on the honeycomb by the same method as in Example 1 (2), and 100 g of the dry powder of Ir-Z was coated per liter of the honeycomb volume.
An r-Na / SiC catalyst coated honeycomb (A-4) was obtained.

Example 5 Preparation of catalyst-coated honeycomb A-5: In Example 1 (1), 0.8 g of magnesium metal was used instead of potassium chloride.
1.2 wt% Ir-1.8 wt% Zr-0.8 wt% Mg (Ir) in terms of metal in the same manner as in Example 1 (1) except that magnesium chloride (MgCl ₂ ) corresponding to /
Zr / Mg = 1 / 3.2 / 5.3 (atomic ratio)) / SiC catalyst powder was obtained.

The above catalyst powder was wash-coated on a honeycomb in the same manner as in Example 1 (2), and 100 g of the dry powder of Ir-Z was coated per liter of the honeycomb volume.
An r-Mg / SiC catalyst coated honeycomb (A-5) was obtained.

Example 6 Preparation of catalyst-coated honeycomb A-6: Example 1 (1) except that barium chloride (BaCl ₂ ) corresponding to 0.8 g of metal barium was used in place of potassium chloride. In the same manner as 1 (1), 1.2 wt% Ir in terms of metal
-1.8 wt% Zr-0.8 wt% Ba (Ir / Zr / B
a = 1 / 3.2 / 0.9 (atomic ratio)) / SiC catalyst powder was obtained.

The catalyst powder was wash-coated on the honeycomb by the same method as in Example 1 (2), and 100 g of the dry powder of Ir-Z was coated per liter of the honeycomb volume.
An r-Ba / SiC catalyst coated honeycomb (A-6) was obtained.

Example 7 Preparation of catalyst-coated honeycomb A-7: In Example 1 (1), metal titanium 1.8 was used instead of zirconium chloride oxide.
titanium sulfate [Ti (SO ₄ ) ₂ ] solution (Ti
1.2 wt% Ir-1.8 wt% Ti in terms of metal in the same manner as in Example 1 (1) except that the content ratio was 30%).
-0.8 wt% K (Ir / Ti / K = 1 / 6.0 / 3.3
(Atomic ratio)] / SiC catalyst powder was obtained.

The catalyst powder was wash-coated on a honeycomb in the same manner as in Example 1 (2), and 100 g of dry-converted Ir-T per 1 liter of honeycomb volume was coated.
An i-K / SiC catalyst-coated honeycomb (A-7) was obtained.

Comparative Example 1 Preparation of Catalyst-Coated Honeycomb B-1: Example 1 (1) except that SiC powder was 98.8 g and zirconium chloride oxide and potassium chloride (KCl) were not used. 1.2% by weight in terms of metal I in the same manner as 1 (1)
A powder of r / SiC catalyst was obtained.

A honeycomb was wash-coated with the above catalyst powder in the same manner as in Example 1 (2), and 100 g of dry-converted Ir / S was coated per liter of honeycomb volume.
An iC catalyst-coated honeycomb (B-1) was obtained.

Comparative Example 2 Preparation of Catalyst Coated Honeycomb B-2: In Example 1 (1), SiC powder was adjusted to 97.0 g and potassium chloride (KC
1.2% by weight Ir-1.8% by weight Zr (I) in terms of metal in the same manner as in Example 1 (1) except that 1) was not used.
r / Zr = 1 / 3.2 (atomic ratio)) / SiC catalyst powder was obtained.

The catalyst powder was wash-coated on the honeycomb in the same manner as in Example 1 (1), and 100 g of the dry powder of Ir-Z was coated per liter of the honeycomb volume.
An r / SiC catalyst-coated honeycomb (B-2) was obtained.

Comparative Example 3 Preparation of Catalyst-Coated Honeycomb B-3: Same as Example 1 (1) except that 98.0 g of SiC powder was used and no zirconium chloride oxide was used in Example 1 (1). Then, 1.2 wt% Ir-0.8 wt% K (Ir
/K=1/3.3 (atomic ratio)) / SiC catalyst powder was obtained.

Ir-K was coated with 100 g of dry-converted honeycomb per 1 liter of honeycomb by wash-coating the above-mentioned catalyst powder on the honeycomb in the same manner as in Example 1 (2).
A / SiC catalyst coated honeycomb (B-3) was obtained.

Comparative Example 4 Preparation of Catalyst-Coated Honeycomb B-4: In Example 1 (1), SiC powder was 98.0 g, and zirconium chloride oxide was not used, and metallic magnesium was used in place of potassium chloride. 8 g of magnesium chloride (MgCl ₂ )
1.2 wt% Ir-0.8 wt% Mg (Ir / Mg = 1) in terms of metal in the same manner as in Example 1 (1) except that
/5.3 (atomic ratio)) / SiC catalyst powder was obtained.

The catalyst powder was wash-coated on the honeycomb in the same manner as in Example 1 (2), and 100 g of the dry powder of Ir-M was coated per liter of the honeycomb volume.
A g / SiC catalyst-coated honeycomb (B-4) was obtained.

Test Example 1 Performance evaluation by model exhaust gas: Catalyst-coated honeycombs (A-1 to A-7) obtained in Examples 1 to 7 and Comparative Examples 1 to 4
Regarding the catalyst-coated honeycombs (B-1 to B-4) obtained in
NO using model exhaust gas (A) to (C) having the following composition
x Reduction performance was evaluated.

That is, each model exhaust gas is supplied to the gas space velocity.
Honeycomb while flowing at GHSV 38,000 / hr
Inlet temperature from 200 ℃ to 600 ℃ (C as reducing agent
_ThreeH₆ 100 ° C for model exhaust gas (A) using
Temperature up to 600 ° C) and the temperature is continuously raised at a rate of 30 ° C / min.
The NOx concentration of the gas flowing out at the catalyst outlet in the meantime
Continuous measurement was performed with a luminescent NOx meter. This measured catalyst
NOx value at the outlet (B) and exhaust collected from the catalyst inlet
Based on the NOx concentration value (A) in the gas,
To obtain the NOx conversion rate by each catalyst coated honeycomb
Was. Maximum NOx conversion for each model exhaust gas
The rates are shown in Table 1.

[0061] A: Catalyst inlet NOx concentration B: Catalyst outlet NOx concentration

Model exhaust gas composition: Model exhaust gas (A) NO 500 ppm C ₃ H ₆ 1,500 ppm C ^* O ₂ 5% H ₂ O 10% N ₂ balance * "ppmC" in the composition is the concentration in terms of methane. It shows (following, the same).

Model Exhaust gas (B) NO 500 ppm Kerosene 2,500 ppm C O ₂ 10% H ₂ O 10% N ₂ balance

Model Exhaust gas (C) NO 500 ppm Light oil 2,500 ppm C O ₂ 10% H ₂ O 10% N ₂ balance

Result: ** The reducing agent in each model exhaust gas is C ₃ H ₆ in (A), kerosene in (B), and light oil in (C).

From the results shown in Table 1, the catalyst-coated honeycombs A-1 to A-7 of the present invention were compared with any of the catalyst-coated honeycombs B-1 to B-4 of Comparative Examples regardless of the kind of the reducing agent. However, it can be seen that the conversion of nitrogen oxides is excellent even in the presence of a large excess of oxygen, compared to the stoichiometric amount of O2 concentration of 5 to 10%.

Test Example 2 Evaluation of durability performance by model exhaust gas: Catalyst-coated honeycombs (A-1 to A-3) obtained in Examples 1 to 3 and Comparative Example 1
The catalyst-coated honeycombs (B-1 to B-3) obtained in Nos. 3 to 3 were tested for durability against high-temperature steam and SOx.

First, with respect to the model exhaust gas (D) having the following composition, the maximum conversion rate of NOx was determined by the same method as in Test Example 1. Next, the honeycomb inlet gas temperature was fixed at 700 ° C., and a model exhaust gas (E) having the following composition was flown at a gas space velocity GHSV 500 / hr for 5 hours to carry out a durability treatment. Furthermore, the maximum conversion rate of NOx in the model exhaust gas (D) was again obtained, and steam and S at 700 ° C.
The influence of the model exhaust gas containing O ₂ was investigated, and the durability of each catalyst-coated honeycomb was obtained. The results are shown in Table 2.

Model exhaust gas composition: Model exhaust gas (D) NO 500 ppm NO2, 2500 ppm CO ₂ 5% H ₂ O 10% N ₂ balance

Model exhaust gas (E) SO ₂ 250 ppm O ₂ 3% H ₂ O 10% N ₂ balance

Result:

As is clear from the results shown in Table 2, the catalyst-coated honeycombs A-1 to A-3 of the present invention not only exhibit excellent initial performance with respect to NOx removal, but also a model containing high-temperature steam and SO _2. It was also resistant to exhaust gas and exhibited high NOx removal performance even after treatment with this exhaust gas. On the other hand, the catalyst-coated honeycomb B-1 of the comparative example
Each of ~ B-3 not only showed insufficient initial activity for NOx removal, but was also affected by high temperature steam and model exhaust gas containing SO ₂ , and the NOx removal performance was further reduced.

As shown in both of the above test examples, the catalyst of the present invention exhibits excellent NOx removal performance as a denitration catalyst even when a wide variety of reducing agents from C ₃ H ₆ to kerosene and light oil are used. A wide range of hydrocarbons, including paraffins, olefins, aromas, naphthenes, and other hydrocarbons with a carbon number of 2 to 25, can be used as a reducing agent for NOx, and to the water vapor and SOx contained in exhaust gas. It is clear that the durability is excellent.

[0074]

According to the catalyst of the present invention, the nitrogen oxides in the exhaust gas containing oxygen in excess of the stoichiometric amount, which has been difficult to obtain by the conventional exhaust gas purifying catalyst, can be converted into hydrocarbons. It can be reduced and removed without dependence. Further, the catalyst of the present invention has excellent durability against water vapor and SOx contained in exhaust gas, and is expected to be usable as a catalyst having a long life. Therefore, the catalyst of the present invention and the purification method of the present invention using the same are useful for purification of exhaust gas discharged from various internal combustion engines, boilers, gas turbines and the like. that's all

Claims (6)

[Claims] 1. A carrier made of silicon carbide, selected from the group consisting of (a) iridium, (b) at least one element selected from the titanium group, and (c) an alkali metal and an alkaline earth metal. An exhaust gas purifying catalyst, which carries at least one element. 2. An element selected from the titanium group of (b),
The exhaust gas purifying catalyst according to claim 1, which is zirconium or titanium. 3. The exhaust gas purifying catalyst according to claim 1, wherein the element selected from the alkali metals and alkaline earth metals of (c) is potassium or sodium. 4. The exhaust gas purifying catalyst according to claim 1, wherein the element selected from the alkali metal and the alkaline earth metal of (c) is magnesium or barium. 5. The exhaust gas purifying catalyst according to claim 1, which is coated on a refractory support substrate. 6. A reducing component containing hydrocarbon and exhaust gas containing oxygen and nitrogen oxide in excess of the stoichiometric amount required to oxidize the reducing component. A method for purifying exhaust gas, which comprises bringing the catalyst into contact with the catalyst according to any one of items 5.