JP2000342972A - Catalyst for purifying exhaust gas and exhaust gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a high nitrogen oxide decomposing activity for a long period of time by a method wherein an exhaust gas purifying catalyst for decomposing nitrogen oxides in the presence of methane under oxygen excess atmosphere is prepared by mixing sulfate group-containing zirconia carrying palladium and inorganic support carrying platinum. SOLUTION: For preparing a catalyst to decompose nitrogen oxide, which is contained in an exhaust gas and exerts a bad influence on the environment, using methane under oxygen excess atmosphere, a catalyst prepared by mixing sulfate group-containing zirconia carrying palladium and inorganic support carrying platinum is used. And an inorganic carrier to be used comprises at least one of material selected from the group consisting of zirconia, zirconia having sulfate group, and titania, and the amount of palladium to be carried is set within a range of 0.1-0.5 wt.% with respect to zirconia having sulfate group. By using such an exhaust gas purifying catalyst, nitrogen oxides can be purified for a long period in a stable manner using methane as a reducing agent even under conditions that activity inhibiting substances such as water vapor, sulfur oxides, etc. are present.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to is contained in the exhaust gas, nitrogen was used to decompose the catalyst and the catalyst with methane nitrogen oxides adversely affect the environment (NO _x) in an oxygen excess atmosphere The present invention relates to a method for purifying oxides.

[0002] In the present invention, "oxygen excess atmosphere" means that the gas to be treated brought into contact with the catalyst of the present invention is necessary for completely oxidizing the reducing components such as hydrocarbons and carbon monoxide contained therein. It means that the gas contains an oxidizing component such as oxygen or nitrogen oxide in an amount equal to or more than the amount.

[0003]

2. Description of the Related Art A catalyst for reducing nitrogen oxides in an atmosphere of excess oxygen using a hydrocarbon as a reducing agent is disclosed in Japanese Patent Application Laid-Open No. 63-100919.
And Japanese Patent Application Laid-Open No. 1-135541.
However, these known references do not disclose the use of methane as a hydrocarbon.

[0004] Methane is present in exhaust gases generated when various fuels are burned. Furthermore, since methane is a major component of natural gas-based city gas that is widely supplied to households and factories in Japan, if it can be used to reduce nitrogen oxides, it must be placed in an oxidizing atmosphere. This is a very effective means for reducing nitrogen oxides.

Japanese Patent Application Laid-Open No. 5-192382 discloses a method for reducing nitrogen oxides in exhaust gas by bringing combustion exhaust gas into contact with a zeolite catalyst in which cobalt or rhodium has been ion-exchanged in the presence of methane. . However, the activity of this catalyst is not sufficient, and further, there is no mention of the activity of the catalyst in the presence of steam which is always contained in actual combustion exhaust gas. That is, it is well known that steam reduces the catalytic activity in a reaction of reducing nitrogen oxides under an oxidizing atmosphere using a hydrocarbon as a reducing agent. There is no indication of the decline and measures to address it.

JP-A-6-254352 discloses that a catalyst in which palladium is supported on a ZSM-5 type zeolite by ion exchange is active in reducing and removing nitrogen oxides using methane as a reducing agent. However, this publication does not disclose the activity of the catalyst in the presence of steam.

Japanese Patent Publication No. Hei 8-500772 discloses that a catalyst in which 0.3 to 2% by weight of palladium is supported on an MFI-type zeolite by ion exchange can be used to reduce nitrogen oxidation even in the presence of steam using methane as a reducing agent. It is disclosed that the compound exhibits a reducing activity of the product. Satokawa et al. Reported in the 1996 Preparatory Meeting on Catalyst Research Presentations (published on September 13, 1996) that a catalyst obtained by ion-exchanging palladium with mordenite showed high nitrogen oxide reduction even in the presence of steam. It discloses that it exhibits activity. However, these catalysts
In the presence of steam, there is a problem that the activity is greatly reduced with time. For example, Hoshi et al. Reported the durability of mordenite in the presence of water vapor for a catalyst in which palladium was ion-exchanged in the 1997 Preparatory Meeting on Catalyst Research Presentations (issued August 25, 1997). I have.
According to this report, the removal rate of nitrogen oxides, which was about 50% at the start of the reaction, rapidly decreased to 30% after 40 hours.
And after 70 hours, it is 15%.

[0008] For carriers other than zeolites, Resasco et al. Have applied Applied Catalysis B:
Environmental (Applied Catalysis B: Enviro
nmental, Vol. 7, page 113 (1995), reports the results of reducing nitrogen oxides with methane as a reducing agent using a catalyst in which palladium is supported on sulfated zirconia.
However, according to the graph showing the change over time of the catalyst activity described therein, the activity of this catalyst shows a clear tendency to deteriorate within a short time of about 100 minutes even in the absence of steam. ing.

As apparent from the above, the conventional nitrogen oxide decomposing catalyst has a problem that its activity is significantly deteriorated by the presence of water vapor, so that steam is inevitably present. In treating flue gas, a high denitration rate cannot be maintained for a long time.

[0010] Furthermore, in the combustion exhaust gas, there is a trace amount of sulfur oxides derived from a trace amount of organic sulfur in the fuel. It is also known to have a cumulative negative effect on the activity and gradually reduce its activity (eg,
Nishizaka et al., Proceedings of 1997 Catalyst Research Presentations, 1997
August 25, 2008).

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an exhaust gas purifying method which can stably purify nitrogen oxides over a long period of time using methane as a reducing agent even in the presence of an activity inhibitor such as steam or sulfur oxide. The main purpose is to provide a catalyst for use.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies while paying attention to the state of the art as described above, and as a result, have found that palladium supported on a sulfated zirconia support and platinum supported on an inorganic support are distinguished from each other. A mixed catalyst (hereinafter, referred to as
"Sometimes referred to as a" mixed catalyst ") when decomposing and removing nitrogen oxides using methane as a reducing agent, to maintain high nitrogen oxide decomposition activity for a long time.

The present invention has been completed based on such new findings and provides the following exhaust gas purifying catalyst and exhaust gas purifying method. 1. It is characterized by being mixed with a sulfated zirconia carrying palladium and an inorganic carrier carrying platinum.
An exhaust gas purification catalyst that decomposes nitrogen oxides in the presence of methane in an oxygen-excess atmosphere. 2. Item 2. The exhaust gas purifying catalyst according to Item 1, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia, and titania. 3. Item 3. The exhaust gas purifying catalyst according to Item 2, wherein the inorganic carrier is sulfated zirconia. 4. Item 4. The exhaust gas-purifying catalyst according to any one of Items 1 to 3, wherein the supported amount of palladium is 0.1 to 0.5% by weight relative to sulfated zirconia. 5. An exhaust gas purification method for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere using a catalyst comprising a mixture of sulfated zirconia carrying palladium and an inorganic carrier carrying platinum. 6. Item 6. The exhaust gas purification method according to Item 5, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia, and titania. 7. Item 7. The exhaust gas purifying method according to Item 6, wherein the inorganic carrier is sulfated zirconia. 8. Item 8. The exhaust gas purifying method according to any one of Items 5 to 7, wherein the amount of palladium carried in the catalyst is 0.1 to 0.5% by weight based on the sulfated zirconia. 9. Exhaust gas that decomposes nitrogen oxides in exhaust gas containing excess oxygen and sulfur oxides in the presence of methane using a catalyst composed of a mixture of sulfated zirconia carrying palladium and an inorganic carrier carrying platinum Purification method. Ten. Item 10. The method for purifying exhaust gas according to Item 9, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia, and titania. 11． Item 10. wherein the inorganic carrier is sulfated zirconia.
2. The exhaust gas purification method according to 1. 12． Item 12. The method for purifying exhaust gas according to any one of Items 9 to 11, wherein the supported amount of palladium in the catalyst is 0.1 to 0.5% by weight relative to sulfated zirconia.

The catalyst according to the present invention can be obtained by mixing a catalyst in which palladium is supported on sulfated zirconia and a catalyst in which platinum is supported on an inorganic carrier.

The sulfated zirconia itself used as a carrier for palladium is a known substance (for example, Makoto Hino and Kazushi Arata, "Surface", Vol. 28, No. 7, page 481 (1990);
See “Surface”, Vol. 34, No. 2, page 51 (1996)). That is, sulfated zirconia is obtained, for example, by immersing commercially available zirconium hydroxide in dilute sulfuric acid, or impregnating zirconium hydroxide with an aqueous solution of ammonium sulfate, and then in air.
It is obtained by firing at about 450 to 650 ° C, more preferably at about 500 to 600 ° C. If the firing temperature is too high, the sulfate groups may volatilize and disappear in large quantities, whereas if the firing temperature is too low, the effect of the firing becomes insufficient, and unreacted zirconium hydroxide is present in the carrier. It remains or the fired body becomes amorphous, and stable sulfate zirconia is not formed. During the firing operation,
Since a part of the sulfate groups is volatilized, it is preferable to add an excessive amount of sulfate groups corresponding to the volatile matter to zirconium hydroxide during the above treatment or impregnation.

Sulfate Sulfate (SO ₄ ^2- ) in zirconia carrier
Is usually 1 to 20 based on the weight of zirconia.
%, More preferably about 3 to 10%. When the amount of sulfate is too small, the effect of supporting sulfate is not sufficiently exhibited, while when it is excessive, a stable sulfate zirconia carrier cannot be obtained.

Examples of the inorganic carrier for supporting platinum include:
For example, zirconia, titania, tungsten zirconia, sulfate zirconia, alumina, silica, silica-alumina, crystalline aluminosilicate, and the like can be used. Among these inorganic carriers, zirconia, titania, tungsten zirconia, sulfate zirconia and the like are more preferable in consideration of activity, durability and the like. As zirconia, titania, alumina, and the like, commercially available catalyst carriers can be used as they are. Also,
The zirconia support can also be easily prepared by calcining zirconium hydroxide. Tungsten zirconia is a known substance that may be described as WO ₃ / ZrO ₂ (for example, Makoto Hino and Kazushi Arata, “Surface”, Vol. 34, No. 2)
51 (1996)) according to known methods.

The method of supporting palladium on the nitrate zirconia carrier is not particularly limited as long as the palladium is supported on the carrier in a highly dispersed state, but is preferably carried out by impregnating the carrier with an aqueous solution of a nitrate, an ammine complex or the like. . The supported amount of palladium is usually about 0.05 to 1%, more preferably about 0.1 to 0.5%, based on the weight of sulfated zirconia. If the amount of supported palladium is too small, the catalytic activity will be low, whereas if it is too large, the catalytic activity will be rather lost due to aggregation.

The method of supporting platinum on the inorganic carrier can be carried out in the same manner as described above. The amount of platinum supported on the inorganic carrier is usually about 10 to 200%, more preferably about 20 to 100%, based on the weight of palladium, as the platinum content in the mixed catalyst.
When the amount of platinum is too small, the catalytic activity decreases, whereas when it is too large, the activity of removing nitrogen oxides rather decreases. The amount of platinum supported on the inorganic carrier to achieve the above-mentioned preferred ratio of platinum / palladium varies depending on the mixing ratio of the palladium / sulfuric acid zirconia carrier and the platinum / inorganic carrier. Usually, platinum is about 0.05 to 5%, more preferably 0.1 to 5%.
About 1%. When the amount of platinum supported on the inorganic carrier is too small, the activity is low. On the other hand, when the amount is too large, the platinum particles are coarsened, and the activity corresponding to the amount of supported platinum may not be obtained.

The palladium-supported sulfate zirconia and the platinum-supported inorganic carrier are all dried,
Bake. If the calcination temperature is too low, the effect of calcination becomes insufficient and stable catalytic activity is hardly obtained, whereas if it is too high, aggregation of palladium and platinum is promoted. Therefore, the firing temperature is usually 300-600 ° C.
Degree, more preferably in the range of about 450 to 550 ° C.

Then, the mixed catalyst of the present invention is obtained by mixing the sulfate-supported zirconia carrying palladium and the inorganic carrier carrying platinum prepared as described above. Alternatively, if necessary, both may be mixed after each drying step, and the resulting mixture may be fired. Alternatively, after performing the molding step described below using the dry mixture, baking may be performed. Regardless of which mixing method is used, it is desirable to perform mixing sufficiently to obtain a mixture as uniform as possible in order to achieve the desired effect according to the present invention.

The catalyst of the present invention may be used in the form of pellets according to a conventional method, or may be wash-coated on a refractory honeycomb carrier. In any case, a binder can be added as needed.

The method for purifying exhaust gas according to the present invention is characterized by using the mixed catalyst obtained above. When the amount of the catalyst used is too small, an effective nitrogen oxide purification rate cannot be obtained, whereas when it is too large, the performance corresponding to the amount of the catalyst used cannot be obtained. Therefore, the catalyst is preferably used in a range where the gas hourly space velocity (GHSV) is 2,000 to 200,000 h ^-1, and more preferably in a range where 2,000 to 60,000 h ^-1 .

Although the catalyst of the present invention has a high activity, if the temperature of the exhaust gas is still too low, effective purification performance may not be exhibited. On the other hand, if the temperature of the exhaust gas is too high, the durability of the catalyst may be impaired. Therefore, it is desirable to use the catalyst according to the present invention in the range of about 350 to 500 ° C, more preferably in the range of about 375 to 475 ° C.

The concentration of nitrogen oxides in the exhaust gas to be purified by the method of the present invention is not particularly limited, but is usually 10 to 5000 vol.
It is in the ppm range. The methane concentration during nitrogen oxide decomposition is
Although it may vary depending on the required denitration rate and other reaction conditions, in order to obtain a high denitration rate, the concentration of nitrogen oxides in the exhaust gas should be generally at least 1 times, more preferably at least 5 times. Is more preferred. When the amount of methane contained in the exhaust gas is smaller than that required for the reduction of nitrogen oxides, an appropriate amount of methane or a methane-containing gas such as a natural gas-based city gas may be added to the exhaust gas. There is no particular upper limit on the methane concentration, and the higher the concentration, the higher the denitration rate. However, even if an excessive amount of methane is added to the exhaust gas, the nitrogen oxide decomposition rate is not improved in proportion to the accompanying increase in cost, and this is economically disadvantageous. May be increased. Furthermore, since the gas to be treated needs to be in an oxygen excess state in a state where methane as a reducing agent is added, the amount of methane to be added has an upper limit determined according to the composition of the gas to be treated.

The oxygen concentration in the exhaust gas is not particularly limited as long as it contains excessive oxygen. When the oxygen concentration is extremely low, for example, when the oxygen concentration is 1% or less on a volume basis, sufficient reaction activity is obtained. May not be possible. If the oxygen concentration in the exhaust gas is too low or if the temperature of the exhaust gas is high and the temperature of the catalyst may exceed the preferred temperature range, while taking care that the exhaust gas temperature does not fall below the preferred range, After mixing an appropriate amount of air, the air mixed gas may be brought into contact with the catalyst.

[0027]

When, according to the present invention using the catalyst of the present invention to process the nitrogen oxides-containing exhaust gas, when NO _x decomposition and removal of methane as a reducing agent, even under conditions where water vapor is present in large quantities, stable over time The resulting catalytic activity is obtained.

Also, since the conversion rate of methane is maintained at a high level, the concentration of residual methane in the processing gas can be kept low.

Further, even in the presence of a sulfur oxide, the activity of which is significantly reduced in the conventional catalyst, a high catalytic activity is stably maintained.

[0030]

EXAMPLES Hereinafter, the features of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 Preparation of Catalyst (1) 360 g of zirconium hydroxide was impregnated with 400 g of an aqueous solution in which 54 g of ammonium sulfate was dissolved for 15 hours. After drying the impregnated body, it was calcined at 550 ° C. for 6 hours to obtain sulfated zirconia.
As a result of inductively coupled plasma-emission spectroscopy, the obtained sulfate zirconia contained 2.2% by weight of sulfate as S.

35 g of the sulfated zirconia obtained above was immersed in a solution obtained by diluting 1.75 g of a palladium nitrate solution containing 10% by weight as Pd with pure water to 30 ml for 15 hours, dried, and then dried at 500 ° C. By calcining for 9 hours, 0.5% Pd / sulfate radical zirconia was obtained.

On the other hand, to a solution prepared by diluting 3.0 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt with pure water to 30 ml was added sulfate zirconia 35 prepared in the same manner as described above.
g was immersed for 15 hours, dried, and calcined at 500 ° C. for 9 hours to obtain 0.5% Pt / sulfate radical zirconia.

Next, 0.5% Pd /
7.5 g of sulfated zirconia and 0.5% Pt / 2.5 g of sulfated zirconia
Was thoroughly mixed in a mortar to obtain a catalyst (1). Example 2 Preparation of catalyst (2) 160 g of zirconium hydroxide, 20 g of tungstic acid (H ₂ WO ₄ )
And 200 ml of water, and after stirring for 6 hours,
It was kept for a time. The product obtained is dried and 800
C. for 6 hours to obtain tungsten zirconia.

Next, 20 g of the tungsten zirconia obtained above was added to a solution obtained by diluting 1.7 g of an aqueous tetraammineplatinum nitrate solution containing 5.8% by weight of Pt to 15 ml with pure water.
Was immersed for 15 hours, dried, and fired at 500 ° C. for 9 hours to obtain 0.5% Pt / tungsten zirconia.

This 0.5% Pt / tungsten zirconia 2.5 g
And 0.5% Pd / sulfate radical zirconia obtained in the same manner as in Example 1.
The mixture was mixed with 7.5 g in a mortar to obtain a catalyst (2). Example 3 Preparation of Catalyst (3) Zirconium hydroxide was calcined at 700 ° C. for 6 hours to obtain a zirconia support.

15 g of the zirconia obtained above was immersed in a solution prepared by diluting 1.3 g of an aqueous tetraammineplatinum nitrate solution containing 5.8% by weight of Pt with pure water to 15 ml for 15 hours, dried, and dried at 500 ° C. for 9 hours. After firing for 0.5 hour, 0.5% Pt / zirconia was obtained.

The 0.5% Pt / 2.5 g of zirconia and the 0.5% Pd / 7.5 g of sulfated zirconia obtained in the same manner as in Example 1 were mixed in a mortar to obtain a catalyst (3). Example 4 Preparation of Catalyst (4) Amorphous titanium oxide was calcined at 600 ° C. for 9 hours to obtain a titania carrier.

6 g of the titania carrier obtained above was immersed in a solution prepared by diluting 0.5 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt with pure water for 10 hours, dried, and dried at 500 ° C. for 9 hours. After firing for 0.5 hours, 0.5% Pt / titania was obtained.

This 0.5% Pt / titania (2 g) and 0.5% Pd / sulfate sulfate zirconia (6 g) prepared in the same manner as in Example 1 were mixed in a mortar to obtain a catalyst (4). Comparative Example 1 Preparation of Comparative Mixed Catalyst (1) 20 g of tungsten zirconia prepared in the same manner as in Example 2 was immersed in a solution prepared by diluting 1 g of a palladium nitrate solution containing 10% by weight as Pd to 15 ml with pure water for 15 hours. After drying, the mixture was fired at 500 ° C. for 9 hours to obtain 0.5% Pd / tungsten zirconia.

This 0.5% Pd / tungsten zirconia 7.5
g and 0.5 g of 0.5% Pt / 2.5 g of sulfated zirconia prepared in the same manner as in Example 1.
I got Comparative Example 2 Preparation of Comparative Mixed Catalyst (2) 0.5 g of 0.5% Pd / tungsten zirconia prepared in the same manner as in Comparative Example 1 and 0.5% Pt / tungsten prepared in the same manner as in Example 2
2.5 g of tungsten zirconia was mixed in a mortar to obtain a comparative mixed catalyst (2). Example 5 Catalyst activity test 1 Mixed catalysts (1) to (4) obtained in Examples 1 to 4, Comparative examples 1 to
The comparative mixed catalysts (1) and (2) obtained in Step 2, 0.5% Pd / sulfuric acid zirconia (comparative single catalyst A) and 0.5% Pt / sulfuric acid zirconia (comparative single catalyst B) were each tablet-formed. It was pulverized and sized to a particle size of 1 to 2 mm.

Using a reactor filled with 4 ml of each of the obtained granules, 150 ppm of nitric oxide and 2000 pp of methane were used.
Simulated exhaust gas consisting of m, 10% oxygen, 9% water vapor and the balance helium was passed at a gas hourly space velocity (GHSV) of 15,000 h ^-1 and the catalyst layer temperature was varied from 350 ° C to 500 ° C. Then, a catalytic activity test was performed. Methane at the catalyst layer outlet,
The carbon monoxide and carbon dioxide concentration gas chromatography, also the concentration of NO _x catalyst layer inlet and outlet by chemiluminescent NO _x analyzer was measured. In addition, the actual combustion exhaust gas usually contains 5 to 15% of carbon dioxide in addition to the above components, but it has been separately confirmed that this does not substantially affect the reaction activity.

The results are shown in Table 1. In Table 1, NO _x conversion (%) and methane conversion (%) indicates a value calculated by the following.

(NO _x conversion) = 100 × (1-NO _x -out / NO _x -in) (CH ₄ conversion) = 100 × (CO-out + CO ₂ -out) / (CO-out + CO _2-
out + CH ₄ -out) where “NO _x -in” is the NO _x concentration at the catalyst bed inlet, “NO _x -ou
t "is the concentration of NO _x catalyst layer outlet," CO-out "is the concentration of carbon monoxide catalyst layer outlet," CO ₂ -out "the carbon dioxide concentration of the catalyst layer outlet," CH ₄ -out "the catalyst layer Each represents the methane concentration at the outlet.

[0044]

[Table 1]

From the results shown in Table 1, it can be seen that the mixed catalyst according to the present invention is compared with the comparative single catalyst A consisting only of 0.5% Pd / sulfate zirconia and the comparative single catalyst B consisting only of 0.5% Pt / sulfate zirconia. It is evident that it shows significantly higher activity.

Further, even when Pd and Pt are used as active components similarly to the mixed catalyst of the present invention, when a carrier other than sulfated zirconia is used as a Pd carrier (Comparative mixed catalysts (1) and (2) )) Also shows that its nitrogen oxide decomposition activity is not very high. Comparative Example 3 Preparation of Pd / Mordenite Catalyst 60 g of H-type mordenite (manufactured by Tosoh Corporation, silica / alumina ratio: 16) was heated at 60 ° C. using 700 ml of an aqueous solution in which 0.83 g of tetraamminepalladium nitrate and 6 g of ammonium acetate were dissolved. Ion exchange was performed for 18 hours. The ion-exchanged H-form mordenite was separated by filtration, washed, and
Dried for 500 hours at 500 ° C in air for 9 hours.
A mordenite catalyst was obtained. As a result of composition analysis by inductively coupled plasma-emission spectroscopy, the amount of Pd supported on the obtained ion-exchanged H-type mordenite was 0.42%. Example 6 Catalyst Activity Test 2 The catalyst (1) according to Example 1, the catalyst (2) according to Example 2 and the catalyst according to Comparative Example 3 were each tablet-molded, pulverized, and sized to a particle size of 1 to 2 mm. Using a reactor filled with 4 ml of each of the obtained sized particles, a simulated exhaust gas composed of 150 ppm of nitrogen monoxide, 2000 ppm of methane, 10% of oxygen, 9% of steam, 3 ppm of sulfur dioxide and the balance of helium was charged in a space per gas hour. The catalyst was tested under the conditions of a velocity (GHSV) of 15,000 h ^-1 and a catalyst layer temperature of 450 ° C.

[0047] Catalyst (1), for the catalyst (2) and Comparative Example 3 catalyst shows methane and NO _x conversion of the change over time as each view 1, 2 and 3.

As is clear from FIG. 3, a conventionally known mordenite catalyst supporting palladium (Comparative Example 3)
Catalyst) is initially represents the high level of the NO _x decomposition removal performance, causing over time a significant reduction in activity, after about 1 day, losing little activity.

On the other hand, FIG. 1 (catalyst (1)) and FIG.
As is clear from (catalyst (2)), the catalyst according to the present invention
Stably maintain high NO _x conversion over time.

[Brief description of the drawings]

FIG. 1 is a graph showing the change over time of the conversion of NO _x and methane by the catalyst (1) of Example 1 of the present invention.

FIG. 2 is a graph showing the change over time of the conversion of NO _x and methane by the catalyst (2) of Example 2 of the present invention.

FIG. 3 shows NO _{x over} Pd / mordenite catalyst of Comparative Example 3.
4 is a graph showing the change over time of the conversion rate of methane and methane.

Continued on the front page (72) Inventor Masataka Masuda 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture Inside Osaka Gas Co., Ltd. F term in Kyushu Catalyst Research Co., Ltd. (reference) BC72A BC72B BC75A BC75B CA02 CA10 CA13 FB13

Claims (12)

[Claims] An exhaust gas purifying method for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere, comprising a mixture of sulfated zirconia carrying palladium and an inorganic carrier carrying platinum. catalyst. 2. The exhaust gas purifying catalyst according to claim 1, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia and titania. 3. The exhaust gas purifying catalyst according to claim 2, wherein the inorganic carrier is sulfated zirconia. 4. The exhaust gas purifying catalyst according to claim 1, wherein the supported amount of palladium is 0.1 to 0.5% by weight relative to sulfate zirconia. 5. A method for purifying exhaust gas comprising decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere using a catalyst comprising a mixture of sulfated zirconia carrying palladium and an inorganic carrier carrying platinum. 6. The exhaust gas purifying method according to claim 5, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia and titania. 7. The exhaust gas purifying method according to claim 6, wherein the inorganic carrier is sulfated zirconia. 8. The catalyst according to claim 5, wherein the supported amount of palladium in the catalyst is 0.1 to 0.5% by weight with respect to sulfate zirconia.
An exhaust gas purifying method according to any one of claims 7 to 10. 9. Use of a catalyst comprising a mixture of sulfated zirconia carrying palladium and an inorganic carrier carrying platinum to remove nitrogen oxides in exhaust gas containing excess oxygen and containing sulfur oxides in the presence of methane An exhaust gas purification method that decomposes below. 10. The exhaust gas purifying method according to claim 9, wherein the inorganic carrier is at least one selected from the group consisting of zirconia, sulfate zirconia, tungsten zirconia and titania. 11. The exhaust gas purification method according to claim 10, wherein the inorganic carrier is sulfated zirconia. 12. The catalyst according to claim 9, wherein the supported amount of palladium in the catalyst is 0.1 to 0.5% by weight with respect to sulfate zirconia.
An exhaust gas purifying method according to any one of claims 1 to 11.