JP2002301338A - Catalyst for cleaning exhaust gas and method for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst for cleaning exhaust gas which is capable of cleaning nitrogen oxides stably for a long period of time by using methane as a reducing agent even in the presence of stream and sulfur oxide which are a catalytic activity inhibitor. SOLUTION: The catalyst for cleaning exhaust gas by decomposing nitrogen oxides in an oxygen excess atmosphere and in the presence of methane is prepared by supporting at least one component selected from iron, nickel and cobalt, palladium and platinum on a sulfate radical zirconia. In the method for cleaning exhaust gas, nitrogen oxides are decomposed by using the catalyst in the oxygen enriched atmosphere and in the presence of methane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

In the present invention, the terms “oxygen-rich atmosphere” and “exhaust gas containing excess oxygen” refer to the gas to be treated brought into contact with the catalyst according to the present invention, the hydrocarbon contained therein,
This means that the gas contains an oxidizing component such as oxygen or nitrogen oxide in an amount required to completely oxidize a reducing component such as carbon monoxide.

[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 documents do not disclose methane as a usable hydrocarbon.

[0004] Methane is present in exhaust gases generated when various fuels are burned. Furthermore, methane is a main component of natural gas-based city gas widely supplied to households and factories in Japan. Therefore, if nitrogen oxides can be reduced using this, it will be an extremely effective means for reducing nitrogen oxides in an oxidizing atmosphere.

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. Further, no reference is made to the activity of the catalyst in the coexistence of water vapor necessarily 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 a catalyst in which palladium is supported on ZSM-5 type zeolite by ion exchange,
It shows that it has activity in the reduction and removal of nitrogen oxides using methane as a reducing agent. This publication does not disclose the activity of the catalyst in the presence of steam.

Japanese Patent Publication No. 8-500772 discloses that a catalyst in which 0.3 to 2% by weight of palladium is supported on MFI-type zeolite by ion exchange using methane as a reducing agent and high nitrogen oxides even in the presence of steam is used. Are disclosed as having a reducing activity. Satokawa et al. Reported in the 1996 Preliminary 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.

[0008] However, these catalysts have a problem that the activity is rapidly reduced in the presence of steam. For example, Hoshi et al. Reported in the 1997 Preparatory Meeting on Catalyst Research Presentations (published on August 25, 1997) about the catalyst in which mordenite supported palladium by ion exchange.
The durability in the presence of water vapor is reported. 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 15% after 70 hours.

[0009] Regarding the carrier other than zeolite,
Resasco et al. Applied Catalysis Be:
Environmental (Applied Catalysis B: Environ
mental), Vol. 7, page 113 (1995), reports the results of reducing nitrogen oxides using 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 clearly shows a tendency to deteriorate within a short time of about 100 minutes even in the absence of steam. ing.

As clarified above, the conventional nitrogen oxide decomposition catalyst has a problem that the activity is significantly deteriorated by the presence of steam, and therefore, the combustion exhaust gas in which steam is inevitably present. In the process (1), a high denitration rate cannot be maintained for a long time.

Further, 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 that it has an adverse effect on accumulation and gradually reduces its activity (for example, Nishizaka et al., Proceedings of the 1997 Catalysis Research Conference, August 2, 1997
5th).

[0012]

Accordingly, the present invention provides an exhaust gas capable of stably purifying nitrogen oxides over a long period of time using methane as a reducing agent even in the presence of steam and sulfur oxides, which are catalytic activity inhibitors. A main object is to provide a purification catalyst and an exhaust gas purification method.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies while paying attention to the current state of the prior art as described above.
Previously, in a reaction for reducing and removing nitrogen oxides in the presence of methane, it was found that a catalyst comprising platinum zirconia and platinum and palladium supported thereon had high durability (Japanese Patent Application Laid-Open No. 2000-61308).

In a subsequent study, the present inventors have found that, in addition to palladium and platinum, at least one component selected from the group consisting of iron, nickel and cobalt is supported on zirconia sulfate at a high temperature range. Has superior catalytic activity to the above catalyst,
It has been found to exhibit excellent durability.

The present invention has been completed based on such new knowledge, and provides the following exhaust gas purifying catalyst and exhaust gas purifying method. 1. An exhaust gas purifying catalyst for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere, comprising at least one component selected from the group consisting of iron, nickel, and cobalt, and palladium and platinum, on sulfated zirconia. Supported catalyst. 2. An exhaust gas purification method for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere, wherein sulfate zirconia carries at least one component selected from the group consisting of iron, nickel and cobalt, and palladium and platinum. A method using a catalyst. 3. Using a catalyst in which at least one component selected from the group consisting of iron, nickel, and cobalt and palladium and platinum are supported on sulfated zirconia, nitrogen oxides in an exhaust gas containing an excess of oxygen and containing a sulfur oxide are removed. An exhaust gas purification method that decomposes in the presence of methane.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst of the present invention is an exhaust gas purifying catalyst for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere, wherein the sulfate zirconia has a group consisting of iron, nickel and cobalt. And a catalyst carrying at least one component selected from the group consisting of palladium and platinum.

Sulfate zirconia itself is a known substance (for example, Makoto Hino and Kazushi Arata, “Surface”, Vol. 28, No. 7).
No. 481 (1990); “Surface”, Volume 34, No. 2, page 51 (1996)
Etc.). The sulfated zirconia is, for example, by immersing commercially available zirconium hydroxide in dilute sulfuric acid or impregnating zirconium hydroxide with an aqueous solution of ammonium sulfate, evaporating to dryness, and under an oxidizing atmosphere such as in air.
It can be prepared by a method of baking at about 450 to 650 ° C. (preferably about 500 to 600 ° C.) (baking time: about 1 to 20 hours (preferably about 3 to 10 hours). In the case, there is a risk that a large amount of sulfate groups may be volatilized and disappeared.On the other hand, if the amount is too low, the effect of calcination becomes insufficient, and unreacted zirconium hydroxide remains in the carrier, or the calcined product becomes amorphous. During the calcination operation, a part of the sulfate is volatilized, so that an excessive amount of sulfuric acid corresponding to the volatile matter with respect to the zirconium hydroxide during the above-mentioned treatment or immersion is likely to occur. It is preferable to add roots.

Sulfate Sulfate (SO ₄ ^2- ) in zirconia carrier
Content is usually a weight ratio to zirconia (ZrO ₂ )
It is about 1 to 20%, and more preferably about 3 to 10%. If the amount of sulfate is too small, the effect of adding sulfate is not sufficiently exhibited, whereas if the amount is excessive,
A stable sulfate zirconia carrier cannot be obtained.

The specific surface area of the sulfated zirconia is obtained
The catalyst can be used stably and the dispersion of the supported metal can be maintained.
Although not particularly limited as far as possible, the measured value by the BET method
And usually 60-200m^Two/ g, preferably 80-200m^Two/ g
Degrees, more preferably 120-160 m ^Two/ g. Sulfate
The specific surface area of zirconia depends on the supported amount of sulfate,
It can be controlled by the formation temperature and the like.

The catalyst of the present invention contains at least one component selected from the group consisting of iron, nickel and cobalt, in addition to palladium and platinum. For example, a catalyst in which iron, palladium and platinum are supported on sulfated zirconia, a catalyst in which at least one component selected from the group consisting of nickel and cobalt is supported on sulfated zirconia, and palladium and platinum are supported.

The amount of at least one component selected from the group consisting of iron, nickel and cobalt in the catalyst of the present invention (when used together, the total amount thereof) is zirconia (Z
rO ₂ ) by weight, about 0.2 to 4%, preferably 0.5 to
It is about 2%.

The supported amount of palladium in the catalyst of the present invention is usually 0.05 to 1% by weight relative to sulfated zirconia.
Degree, more preferably about 0.1 to 0.5%. If the supported amount of palladium is too small, the catalytic activity may be lowered, whereas if it is too large, the catalytic effect may be lost due to aggregation.

The supported amount of platinum in the catalyst of the present invention is about 10 to 200%, more preferably about 20 to 100% by weight based on palladium. If the supported amount of platinum is too small, the catalytic activity may be reduced,
If it is too high, the activity of removing nitrogen oxides may be reduced.

The method for supporting at least one component selected from the group consisting of iron, nickel and cobalt and palladium and platinum (hereinafter, these components may be referred to as “active components”) on a sulfated zirconia carrier is carried out by the following method. Is not particularly limited, as long as it is highly dispersed on the carrier. For example, the preparation of sulfated zirconia and the loading of the active ingredient may be performed simultaneously, or the active ingredient may be loaded on sulfated zirconia prepared in advance. Alternatively, at least one of the active ingredients may be supported at the same time as the preparation of sulfated zirconia, and then the insufficient active ingredient may be supported. Specifically, first, at the same time as preparing sulfated zirconia, iron, nickel and at least one selected from the group consisting of cobalt is supported, and then the obtained iron and / or nickel and / or cobalt-supported sulfate is supported. A method of supporting palladium and platinum on zirconia can be exemplified. Hereinafter, as a specific example of this method, a method for supporting iron, palladium and platinum, and a method for supporting at least one component selected from the group consisting of nickel and cobalt and palladium and platinum will be described.

Method for supporting iron, palladium and platinum First, zirconium hydroxide is added to an aqueous solution in which ammonium sulfate and a water-soluble iron compound such as iron sulfate and iron nitrate (preferably iron sulfate) are dissolved for 1 to 20 hours. Soak about. After immersion, evaporate to dryness.
By calcining for about 20 hours, iron-supported sulfate zirconia is obtained. The same conditions as those for preparing sulfated zirconia can be applied to the conditions such as the firing temperature.

Next, the obtained iron-supported sulfate zirconia is immersed in a solution of a palladium compound and a platinum compound for about 1 to 20 hours, and evaporated to dryness. As a palladium compound and a platinum compound, when dissolved in a solvent such as water,
The compound is not particularly limited as long as it is a compound that dissociates metal ions of these metals. Such compounds include, for example,
Metal salts such as nitrate and sulfate of palladium or platinum;
Complexes such as ammine complexes and halogen complexes; halides and the like. Specifically, palladium nitrate, tetraamminepalladium nitrate, palladium sulfate, palladium chlorate, tetraammineplatinum nitrate, platinum (IV) chloride
Acid, chloroplatinic (II) acid and the like.
Palladium nitrate and tetraammineplatinum nitrate are preferred. Examples of the solvent for dissolving the active metal compound include water; water-soluble organic solvents such as acetone and ethanol; mixed solvents thereof; and among them, water is preferred.

A method for supporting at least one component selected from the group consisting of nickel and cobalt, and palladium and platinum First, zirconium hydroxide is dissolved in ammonium sulfate and a water-soluble compound such as a sulfate and an acetate of nickel and / or cobalt. It is immersed for about 1 to 20 hours in an aqueous solution in which the compound is dissolved. After immersion, the mixture is evaporated to dryness and fired in an oxidizing atmosphere such as air for about 1 to 20 hours to obtain sulfated zirconia preliminarily supporting nickel and / or cobalt. The same conditions as those for preparing sulfated zirconia can be applied to the conditions such as the firing temperature.

The nickel thus prepared and / or
Or the specific surface area of sulfate zirconia supporting cobalt is usually about 60 to ²⁰⁰ m / g, preferably 80 to ²⁰⁰ m
/ g, more preferably about 120 to 160 m ² / g.

Next, sulfated zirconia supporting cobalt and / or nickel is immersed in a solution of a palladium compound and a platinum compound for about 1 to 20 hours, and evaporated to dryness. As the palladium compound and the platinum compound, the compounds described above can be used. As the solvent for dissolving the active metal compound, the solvents described above can be used.

After drying the sulfated zirconia carrying the active ingredient by the above-mentioned method or the like, if necessary,
It is fired in an oxidizing atmosphere such as in air. The firing temperature is usually about 300 to 600 ° C., more preferably 450 to 5
It is around 50 ° C. If the calcination temperature is too low, the effect of calcination will be insufficient and stable catalytic activity will not be obtained, whereas if it is too high, aggregation of the active components, especially palladium and platinum, will be promoted. The firing time is not particularly limited, but is usually about 1 to 20 hours, preferably about 3 to 10 hours.

The catalyst of the present invention may be formed into an arbitrary shape such as a pellet or a honeycomb according to a conventional method, or may be used by being wash-coated on a refractory honeycomb carrier. In both cases, a binder can be added as needed.

The method for purifying exhaust gas according to the present invention is characterized by using a catalyst in which at least one component selected from the group consisting of iron, nickel and cobalt and palladium and platinum are supported on sulfated zirconia.

Although the amount of the catalyst used is not particularly limited, it is preferably used within a range of about 2,000 to 200,000 h ^-1 at a gas hourly space velocity (GHSV), and is preferably 5,000 to 60,000 h.
It is more preferable to use in the range of about ^-1 . If the amount of catalyst used is too small (GHSV is too large), an effective purification rate cannot be obtained, while the amount of catalyst is too large
When the GHSV is too small, the performance corresponding to the amount of the used catalyst cannot be obtained.

Although the catalyst of the present invention has high activity, if the temperature of the exhaust gas is too low, effective purification performance may not be exhibited. On the other hand, if the temperature of the exhaust gas is too high, there is a risk that the durability of the catalyst is impaired. Therefore, it is desirable to use the catalyst of the present invention at a temperature of preferably about 350 to 550 ° C, more preferably 400 to 525 ° C.

In the composition of the exhaust gas to be purified by the method of the present invention, the concentration of nitrogen oxides is not particularly limited as long as oxygen is excessively contained. The nitrogen oxide concentration in the exhaust gas is
Usually, it is about 10 to 5000 ppm. The methane concentration in the exhaust gas can be appropriately set according to the required denitration rate and other reaction conditions. In order to obtain a high denitration rate, the methane concentration is usually set to be about 1 time or more, more preferably about 5 times or more, of the nitrogen oxide concentration in the exhaust gas.
When the amount of methane contained in the exhaust gas is smaller than the amount 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 may not be improved in proportion to the cost increase, and the amount of methane remaining in the treated gas may be increased. There is. Further, 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 and the like.

The oxygen concentration in the exhaust gas is not particularly limited as long as it contains excessive oxygen. However, when the oxygen concentration is extremely low, for example, when the volume is about 1% or less, sufficient catalytic activity is not obtained. May not be obtained. 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 a predetermined temperature range, take care that the temperature of the exhaust gas does not fall below a suitable range. After mixing the amount of air, the mixed air exhaust gas may be brought into contact with the catalyst.

The exhaust gas usually contains a sulfur oxide. The present invention can be applied to exhaust gas containing such a sulfur oxide.

[0038]

According to the catalyst of the present invention, a high denitration rate can be stably obtained over a long period of time in the removal of NOx using methane as a reducing agent. In particular, the effect is remarkable in a high temperature range.

The exhaust gas usually contains about 5% to 15% of water vapor. According to the method of the present invention, an effective purification performance can be obtained even for an exhaust gas containing water vapor. .

Exhaust gas usually contains sulfur oxides, which are known to significantly reduce the catalytic activity. Since the catalyst of the present invention shows high resistance to the decrease in activity due to the sulfur component, high catalytic performance is maintained for a long period of time.

[0041]

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

Example 1 (Preparation of Catalyst 1) 120 g of zirconium hydroxide (manufactured by Mitsui Chemicals, Inc .; containing 86% by weight as ZrO ₂ ) was 18 g of ammonium sulfate and ferrous sulfate (FeSO ₄ .7H ₂ O). 5 g and 1 ml of sulfuric acid dissolved in an aqueous solution (1
50 ml) for 15 hours. After evaporating this to dryness, it is calcined in air at 550 ° C. for 6 hours to obtain iron-supported sulfate zirconia A.
I got

Next, 0.5 g of a palladium nitrate solution containing 10% by weight as Pd and 0.35 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred, and a solution diluted to 20 ml with pure water was added. Prepared. Iron-supported sulfated zirconia A (20 g) was immersed in this solution for 15 hours. After immersion, the mixture was evaporated to dryness and calcined in air at 500 ° C. for 6 hours to obtain Catalyst 1.

[0044] Example 2 (Preparation of Catalyst 2) zirconium hydroxide (Mitsuwa Chemicals Co., Ltd .; as ZrO ₂ 86 wt% content) 180 g ammonium sulfate 27g and cobalt sulfate _{(CoSO 4 · 7H 2 O)} 7.4g Aqueous solution (200 m
l) for 15 hours. After evaporating it to dryness,
By calcining at 550 ° C. for 6 hours, 1% cobalt-supported sulfate zirconia was obtained.

Then, 0.5 g of a palladium nitrate solution containing 10% by weight as Pd and 0.35 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred, and a solution diluted to 20 ml with pure water was added. Prepared. In this solution, 20 g of the above-mentioned cobalt-supported sulfate zirconia was immersed for 6 hours. After immersion, the mixture was evaporated to dryness and calcined in air at 500 ° C. for 6 hours to obtain Catalyst 2.

Example 3 (Preparation of Catalyst 3) 180 g of zirconium hydroxide (manufactured by Mitsui Chemicals, Inc., containing 86% by weight as ZrO ₂ ) was prepared by 27 g of ammonium sulfate and nickel acetate (Ni (CH ₃ COO) ₂ .4H). ₂ O) 6.6 g dissolved aqueous solution
(200 ml) for 15 hours. After evaporating this to dryness, it was calcined at 550 ° C. for 6 hours in air to obtain 1% nickel-supported sulfate zirconia.

Next, 0.5 g of a palladium nitrate solution containing 10% by weight as Pd and 0.35 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred, and the solution diluted to 20 ml with pure water was added. Prepared. 20 g of the above-mentioned nickel-supported sulfate zirconia was immersed in this solution for 6 hours. After immersion, the mixture was evaporated to dryness and calcined in air at 500 ° C. for 6 hours to obtain Catalyst 3.

Example 4 (Preparation of Catalyst 4) 180 g of zirconium hydroxide (manufactured by Mitsui Chemicals, Inc .; containing 79% by weight as ZrO ₂ ) was mixed with 27 g of ammonium sulfate,
It was immersed for 15 hours in the ferrous sulfate _{(FeSO 4 · 7H 2 O)} 7.5 g and the aqueous solution obtained by dissolving sulfuric acid 1.4 g (180 ml). After evaporating this to dryness, it was calcined at 550 ° C. for 6 hours in air to obtain iron-supported sulfated zirconia B.

Next, 0.875 g of a palladium nitrate solution containing 10% by weight as Pd and 0.61 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred to prepare a solution diluted to 30 ml with pure water. did. The above-mentioned iron-supported sulfated zirconia B (35 g) was immersed in this solution for 15 hours, evaporated to dryness, and calcined at 500 ° C. for 6 hours in air to obtain Catalyst 4.

Example 5 (Preparation of Catalyst 5) 180 g of zirconium hydroxide (manufactured by Mitsui Chemicals, Inc .; containing 79% by weight as ZrO ₂ ) was mixed with 27 g of ammonium sulfate,
Ferrous sulfate _{(FeSO 4 · 7H 2 O)} 7.5 g, cobalt sulfate (CoSO
_{4 · 7H 2 O) 6.8 g} , and the aqueous solution was dissolved sulfate 1.4 g (1
80 ml) for 15 hours. After evaporation to dryness, 550 in air
Calcination was performed at 6 ° C. for 6 hours to obtain sulfated zirconia supporting iron cobalt.

0.75 g of a palladium nitrate solution containing 10% by weight as Pd and 0.52 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred with pure water.
A solution diluted to 28 ml was prepared. In this solution, 30 g of iron-cobalt-supported sulfate zirconia was immersed for 15 hours,
After evaporating to dryness, the mixture was calcined in air at 500 ° C. for 6 hours to obtain Catalyst 5.

[0052] Example 6 (Preparation of catalyst 6) zirconium hydroxide; and (Mitsuwa Chemicals Co., Ltd. as ZrO ₂ 79 wt% content) 240 g, ammonium sulfate 36 g and ferric nitrate (Fe (NO ₃ ) it was immersed for 15 hours in ₃ · 9H ₂ O) 13.2 aqueous solution of the g (210 ml). After evaporation to dryness, in air
By calcining at 575 ° C. for 6 hours, iron-supported sulfated zirconia C was obtained.

0.625 g of a palladium nitrate solution containing 10% by weight as Pd and 0.43 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred to prepare a solution diluted to 21 ml with pure water. . The above-mentioned iron-supported sulfated zirconia C (25 g) was immersed in this solution for 15 hours, evaporated to dryness, and calcined at 500 ° C. for 6 hours in air to obtain a catalyst 6
I got

Example 7 (Preparation of Catalyst 7) 120 g of zirconium hydroxide (manufactured by Mitsui Chemicals, Inc .; containing 79% by weight as ZrO ₂ ) was mixed with 18 g of ammonium sulfate,
Aqueous solution of ferric nitrate _{(Fe (NO 3) 3 ·} 9H 2 O) 13.7 g
(110 ml) for 15 hours. After evaporation to dryness, 55 in air
By calcining at 0 ° C. for 6 hours, iron-supported sulfated zirconia D was obtained.

0.75 g of a palladium nitrate solution containing 10% by weight as Pd, and 0.52 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred with pure water.
A solution diluted to ml was prepared. In this solution, iron-supported sulfated zirconia D (30 g) was immersed for 15 hours, evaporated to dryness, and calcined at 500 ° C. for 6 hours to obtain Catalyst 7.

Reference Example 1 (Preparation of Reference Catalyst 1) A sulfated zirconia A was prepared in the same manner as in Example 1 except that ferrous sulfate and sulfuric acid were not added. 0.94 g of a palladium nitrate solution containing 10% by weight as Pd and 5.8 as Pt
0.65 wt% aqueous tetraammineplatinum nitrate solution
g was mixed and stirred to prepare a solution diluted to 30 ml with pure water. In this solution, sulfated zirconia A (37.5 g) was immersed for 15 hours. After immersion, it was evaporated to dryness and calcined in air at 500 ° C. for 9 hours to obtain Reference Catalyst 1.

Reference Example 2 (Preparation of Reference Catalyst 2) A sulfated zirconia B was prepared in the same manner as in Example 4 except that ferrous sulfate and sulfuric acid were not added. Next, 1.0 g of a palladium nitrate solution containing 10% by weight as Pd and 0.69 g of an aqueous solution of tetraammineplatinum nitrate containing 5.8% by weight of Pt were mixed and stirred to prepare a solution diluted to 35 ml with pure water. To this solution, 15 g of sulfated zirconia B (40 g) was added.
Soaked for hours. After evaporating to dryness, it was calcined in air at 500 ° C. for 6 hours to obtain Reference Catalyst 2.

Example 8 (Catalyst Endurance Test 1 for Catalyst 1) The catalyst 1 prepared in Example 1 was tableted, pulverized, and sized to a particle size of 1 to 2 mm. 4 ml of this catalyst was charged to the catalyst reactor. In this catalytic reactor, 150 ppm of nitric oxide,
Simulated exhaust gas consisting of 2000 ppm of methane, 10% of oxygen, 9% of water vapor and the balance of helium was subjected to gas hourly space velocity (GHSV)
Is 15,000 h ^-1 and the catalyst layer temperature is initially
After a lapse of 70 hours at 450 ° C., the temperature was set at 500 ° C., and the conversion of NOx and methane was measured.

The flue gas usually contains 5 to 15% of carbon dioxide in addition to the components contained in the simulated exhaust gas, but it has been separately confirmed that this does not substantially affect the catalytic activity. did.

The NOx concentration at the inlet and outlet of the catalyst layer was measured by a chemiluminescent NOx analyzer. The conversion (%) of NOx and methane was calculated by the following equation. NOx conversion (%) = 100 × (1 - NOx-out / NOx-in) methane conversion (%) = 100 × (CO -out + CO 2 -out) / (CH 4 -o
ut + CO-out + CO ₂ -out) Here, NOx-in indicates the NOx concentration at the catalyst layer inlet, and NOx-out indicates the NOx concentration at the catalyst layer outlet. CH ₄ -out, CO-out, and CO ₂ -out indicate the methane concentration, carbon monoxide concentration, and carbon dioxide concentration at the catalyst layer outlet, respectively.

FIG. 1 shows the obtained results. As is clear from FIG. 1, the catalyst 1 showed stable catalytic activity over a long period of time even in the presence of steam.

Reference Example 3 (Catalyst durability test of Reference catalyst 1) A durability test was performed on Reference catalyst 1 prepared in Reference example 1 under the same conditions as in Example 8 except that the catalyst layer temperature was maintained at 450 ° C. did. Table 1 shows the results.

As is apparent from Table 1, the NO of reference catalyst 1
The x conversion decreased over time.

[0064]

[Table 1]

Example 9 (Catalyst 1 durability test 2) The catalyst 1 prepared in Example 1 was tableted, pulverized, and sized to a particle size of 1 to 2 mm. 4 ml of this catalyst was charged to the catalyst reactor. In this catalytic reactor, 150 ppm of nitric oxide,
2000 ppm methane, 10% oxygen, 9% steam, 3 ppm sulfur dioxide
A simulated exhaust gas consisting of helium and the balance was circulated so that the space velocity per gas hour (GHSV) was 15,000 h ^-1 , the catalyst layer temperature was set to 450 ° C., and the conversion of NOx and methane was measured. The NOx concentrations at the inlet and outlet of the catalyst layer were measured by a chemiluminescent NOx analyzer. The conversion rates (%) of NOx and methane were determined in the same manner as in Example 8.

FIG. 2 shows the obtained results. As is clear from FIG. 2, the catalyst 1 stably exhibited a high NOx conversion rate over a long period of time even in the presence of steam and sulfur oxides.

Example 10 (Catalyst endurance test 3 of catalyst 1) Conversion of NOx and methane under the same conditions as in Example 9 except that the temperature of the catalyst layer was changed to 500 ° C. for catalyst 1 prepared in Example 1. The rate was measured.

FIG. 3 shows the obtained results. As is clear from FIG. 3, the catalyst 1 stably exhibited a high NOx conversion over a long period of time even under a high temperature condition of 500 ° C.

Example 11 (Catalyst durability test 1 of catalyst 2) A durability test of the catalyst was performed at 450 ° C in the same manner as in Example 9 except that the catalyst 2 prepared in Example 2 was used.

Table 2 below shows the change with time of the NOx conversion rate in the catalyst 2. As is clear from Table 2, the catalyst 2 supporting cobalt instead of iron was the catalyst 1 which is an iron-supporting catalyst.
As in the above, high NOx removal activity was stably exhibited over a long period of time.

[0071]

[Table 2]

Example 12 (Catalyst 2 Durability Test 2) Example 1 was repeated except that the catalyst 2 prepared in Example 2 was used.
The durability test of the catalyst at 500 ° C. was performed in the same manner as in Example 1. The change with time of the NOx conversion is shown in Table 3 below.

As is clear from Table 3, Catalyst 2 exhibited a high NOx removal activity stably over a long period of time at 500 ° C. as in Catalyst 1.

[0074]

[Table 3]

Example 13 (Catalyst 3 durability test) Example 1 was repeated except that the catalyst 3 prepared in Example 3 was used.
The durability test of the catalyst at 500 ° C. was performed in the same manner as in Example 1. FIG. 4 shows changes over time in NOx and methane conversion.

As is evident from FIG. 4, the catalyst 3 showed an increase in NOx removal activity in the initial period of about 20 hours, and thereafter showed a high level of stable catalyst activity over a long period of time.
The catalyst 3 supporting nickel instead of iron also exhibited a high NOx removal activity stably over a long period of time, similarly to the catalyst 1.

Reference Example 4 (Catalyst endurance test of Reference catalyst 1) A reference endurance test of the reference catalyst 1 prepared in Reference example 1 was performed under the same conditions as in Example 10.

FIG. 5 shows the change over time of the NOx and methane conversion rates in the reference catalyst 1. As is clear from FIG.
The NOx conversion rate of the reference catalyst 1 was stable after 20 hours from the start of the test, but remained at about 47%.

Example 14 The catalyst 4 prepared in Example 4 was tableted, pulverized, and sized to a particle size of 1 to 2 mm. 4 ml of this catalyst was charged to the catalytic reactor. A simulated exhaust gas consisting of 150 ppm of nitric oxide, 2000 ppm of methane, 10% of oxygen, 6% of carbon dioxide, 9% of steam, 0.3 ppm of sulfur dioxide, and the balance of nitrogen was introduced into the catalytic reactor at a gas hourly space velocity (GHSV). An endurance test was conducted in which the gas was circulated at 15,000 h ^-1 and the conversion of NOx and methane was measured at a catalyst layer temperature of 450 ° C. NOx
The conversion was calculated in the same manner as in Example 8, and the methane conversion was calculated by the following equation.

(Methane conversion rate) = 100 × (1-CH ₄ -out / CH ₄ -in) Here, CH ₄ -in and CH ₄ -out represent the methane concentration at the inlet and outlet of the catalyst layer, respectively.

Table 4 shows the obtained results. The catalyst 4 exhibited a high denitration rate over a long period of time and exhibited excellent durability.

[0082]

[Table 4]

Example 15 For the catalyst 4, the change over time in the conversion rate of methane and the conversion rate of NOx was measured in the same manner as in Example 14, except that the temperature of the catalyst layer was set at 500 ° C. Table 5 shows the results. Catalyst 4
Even at 500 ° C, maintain a high denitration rate for a long time,
It showed excellent durability.

[0084]

[Table 5]

Example 16 With respect to the catalyst 4, changes with time of the methane conversion rate and the NOx conversion rate were measured in the same manner as in Example 14, except that the temperature of the catalyst layer was changed to 525 ° C. FIG. 6 shows the results. Catalyst 4 is 52
Even at a relatively high temperature of 5 ° C, a high denitration rate was exhibited for a long time.

Example 17 Using the catalyst 5 prepared in Example 5, Example 14
A durability test at 450 ° C. was performed under the same conditions as in the above. Table 6 shows the results. Catalyst 5, which used a combination of iron and cobalt, also exhibited a high NOx conversion over a long period of time, similarly to Catalyst 1 carrying only iron and Catalyst 2 carrying only cobalt.

[0087]

[Table 6]

Example 18 Except that the catalyst 6 prepared in Example 6 was used, the time-dependent changes in the methane conversion and the NOx conversion at 450 ° C. were measured in the same manner as in Example 14. Table 7 shows the results.

The sintering temperature of the iron-supported sulfate zirconia was adjusted to 575.
In the case of the catalyst 6 at ℃, the stabilization of the catalyst activity was quicker and the conversion of methane was excellent as compared with the catalyst 4 (Table 4) in which the calcination temperature was 550 ° C.

[0090]

[Table 7]

Example 19 Using the catalyst 7 prepared in Example 7, Example 14
A durability test at 450 ° C. was performed under the same conditions as described above. Table 8 shows the results.

The catalyst 7 in which the iron content of the sulfated zirconia carrying iron was about 2% by weight relative to zirconia (ZrO ₂ ) was different from the catalyst 4 (Table 4) in which the weight ratio of iron to zirconia was about 1%. Similarly, high denitration rates were shown over time.

[0093]

[Table 8]

Example 20 (Catalyst 2 durability test 3) The same procedure as in Example 14 was carried out except that catalyst 2 was used.
The changes over time of the methane conversion and the NOx conversion at ℃ were measured.

FIG. 7 shows the obtained results. As is clear from FIG. 7, the catalyst 2 showed high catalytic activity over a long period of time.

Reference Example 5 (Catalyst Endurance Test 2 of Reference Catalyst 1) The conversion rate of NOx at 450 ° C. was measured for Reference Catalyst 1 prepared in Reference Example 1 under the same conditions as in Example 14.

Table 9 shows the obtained results. As is evident from Table 9, the catalytic activity of Reference Catalyst 1, which did not contain any of iron, nickel and cobalt, decreased significantly over time.

[0098]

[Table 9]

Reference Example 6 A durability test was performed at 500 ° C. under the same conditions as in Example 15 using Reference Catalyst 2.

Table 10 shows the results. At a relatively high temperature of 500 ° C., the NOx conversion of the reference catalyst 2 containing neither iron, nickel nor cobalt was significantly reduced.

[0101]

[Table 10]

Comparative Example 1 Using the iron-supported sulfated zirconia A prepared in Example 1 (hereinafter sometimes referred to as Comparative Catalyst 1), a durability test was performed at 500 ° C. under the same conditions as in Example 15. .

The NOx conversion after 12 hours from the test was 12%
And the methane conversion was 5%. Similar to Catalyst 1, even though it contained iron and sulfated zirconia, Comparative Catalyst 1 lacking palladium and platinum could not obtain an effective denitration rate even at a relatively high temperature of 500 ° C.

[Brief description of the drawings]

FIG. 1 is a graph showing a change over time in the conversion of NOx and methane of a catalyst 1 according to the present invention (Example 8).

FIG. 2 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 450 ° C. in catalyst 1 according to the present invention (Example 9).

FIG. 3 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 500 ° C. in catalyst 1 according to the present invention (Example 10).

FIG. 4 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 500 ° C. in catalyst 3 according to the present invention (Example 13).

FIG. 5 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 500 ° C. in Reference Catalyst 1 (Reference Example 4).

FIG. 6 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 525 ° C. in Catalyst 4 according to the present invention (Example 16).

FIG. 7 is a graph showing the change over time in the conversion of NOx and methane in the presence of sulfur dioxide at 450 ° C. in catalyst 2 according to the present invention (Example 20).

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Claims (3)

[Claims] 1. An exhaust gas purifying catalyst for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere, comprising at least one component selected from the group consisting of iron, nickel and cobalt in sulfate zirconia; Catalyst supporting palladium and platinum. 2. An exhaust gas purifying method for decomposing nitrogen oxides in the presence of methane in an oxygen-excess atmosphere. A method using a catalyst supporting platinum. 3. An exhaust gas containing an excessive amount of oxygen and containing sulfur oxides using a catalyst in which at least one component selected from the group consisting of iron, nickel and cobalt and palladium and platinum are supported on sulfated zirconia. An exhaust gas purification method for decomposing nitrogen oxides in the presence of methane.