JP2000176250A - Combustion waste gas purifying method and combustion waste gsa purifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify nitrogen oxides stably over a long period of time by using methane as a reducing agent and to suppress the discharge of methane by using a catalyst for decomposing nitrogen oxides in the presence of methane and a catalyst for oxidizing methane in the case where the combustion waste gas containing excess oxygen is purified. SOLUTION: Nitrogen oxides are decomposed in the presence of a catalyst by using methane as a reducing agent, then methane is decomposed in the presence of another catalyst. At this time, the catalyst for reducing the nitrogen oxides is obtained by depositing palladium and platinum on the carrier of sulfate group zirconia. And, the catalyst for oxidizing methane is obtained by depositing palladium and platinum as a catalyst active component on any carrier of zirconia, sulfate group zirconia and tungsten zirconia. The purifying device of combustion waste gas is constituted by providing each reaction device 1 and 2 provided with each catalyst, and also when the methane amount in the waste gas to be treated at the reaction device 1 is too low, an injection device 3 for previously adding the methane to the waste gas is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing nitrogen oxides (NOx) contained in a combustion exhaust gas containing an excessive amount of oxygen and adversely affecting the environment, and an apparatus therefor.

In the present invention, the term "combustion exhaust gas containing excessive oxygen" means that the combustion exhaust gas treated according to the present invention completely oxidizes the reducing components such as hydrocarbons and carbon monoxide contained therein. Means that the gas contains an oxidizing component such as oxygen or nitrogen oxide in an amount more than necessary.

[0003]

2. Description of the Related Art Nitrogen oxides contained in flue gas are:
It is harmful to the human body and is one of the causative agents of acid rain that deteriorates the natural environment. Therefore, its reduction is an urgent technical issue. At present, a so-called three-way catalyst is used for treating nitrogen oxides in automobile exhaust gas, and an ammonia selective reduction method is widely used for treating nitrogen oxides in exhaust gas from power generation facilities and the like. However, the former can be applied only to exhaust gas treatment at a stoichiometric air-fuel ratio in which no excess oxygen remains in the exhaust gas, and the latter has a risk that toxic and strongly odorous ammonia is discharged into the atmosphere.

In view of such circumstances, a catalyst has been proposed which uses a hydrocarbon as a reducing agent to reduce nitrogen oxides in the presence of excess oxygen (JP-A-63-100919; -
No. 135541). Furthermore, an exhaust gas treatment method in which a specific catalyst is brought into contact with an exhaust gas containing nitrogen oxides in the presence of hydrocarbons in an oxidizing atmosphere in which excess oxygen is present, and the exhaust gas is further contacted with an oxidation catalyst, has also been proposed. (See JP-A-4-90826). However, these known documents do not indicate the use of methane as a reducing agent.

[0005] Methane is present in the exhaust gas generated when burning various fuels. 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 becomes possible to reduce nitrogen oxides using it, it will be necessary to use it in an oxidizing atmosphere. This is an extremely effective means for reducing nitrogen oxides.

However, it has been considered difficult to reduce nitrogen oxides in exhaust gas containing reaction inhibiting substances such as water vapor and sulfur oxides using methane as a reducing agent. For example, in a durability test of a catalyst obtained by ion-exchanging palladium with mordenite in the presence of water vapor, the stars rapidly reduced the nitrogen oxide removal rate, which was about 50% at the start of the reaction, and after 40 hours, 30%, 15 after 70 hours
%, Which indicates that nitrogen oxides cannot be removed stably (Preliminary proceedings of the 1997 Catalysis Research Conference; published August 25, 1997).

A major problem when using methane as a reducing agent for nitrogen oxides is that methane is a chemically stable hydrocarbon, and it is difficult to remove it by oxidation. Methane, unlike ammonia,
It is believed that it is substantially non-toxic and poorly photochemically reactive and will not significantly degrade the global atmospheric environment. However, from the viewpoint of global environmental protection in the future, it is desirable to reduce the emission as much as possible.

[0008] In the oxidative decomposition of hydrocarbons, it is known that a catalyst supporting a platinum group metal exhibits high activity. However, since the combustion exhaust gas contains a reaction inhibitor such as water vapor or sulfur oxide, it is inevitable that the catalytic activity decreases with time. For example, Lampe
(rt) et al. report that when methane is oxidized using a palladium catalyst, only 0.1 ppm of sulfur dioxide in methane loses its catalytic activity within hours. Applied Catalysis B: Environmental, Vo
l.14, pp211-223 (1997)).

As apparent from the above, it has been practically impossible to use methane as a reducing agent in the conventional nitrogen oxide decomposition, and it was also difficult to decompose and remove methane itself.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new exhaust gas purification technique which can stably purify nitrogen oxides for a long time using methane as a reducing agent and can suppress methane emission. The main purpose is.

[0011]

Means for Solving the Problems The present inventor has conducted intensive studies while paying attention to the above-mentioned state of the art, and as a result, has found that decomposition of nitrogen oxides in the presence of a first catalyst using methane as a reducing agent. After performing the treatment, it has been found that the above object can be achieved when the methane is decomposed in the presence of the second catalyst.

The present invention has been completed on the basis of such new findings, and provides the following combustion exhaust gas purification method and exhaust gas purification apparatus. 1. A method for purifying a combustion exhaust gas containing an excessive amount of oxygen, comprising using a first catalyst for decomposing nitrogen oxides in the presence of methane and a second catalyst for oxidizing methane. . 2. Item 2. The method for purifying combustion exhaust gas according to Item 1, wherein the combustion exhaust gas is a natural gas combustion exhaust gas. 3. 3. The method for purifying combustion exhaust gas according to the above item 1 or 2, wherein methane is added to the combustion exhaust gas before contacting the combustion exhaust gas with the first catalyst. 4. Item 4. The method for purifying combustion exhaust gas according to any one of Items 1 to 3, wherein the first catalyst is a catalyst in which palladium and platinum are supported on a sulfated zirconia carrier. 5. Item 5. The method according to any one of Items 1 to 4, wherein the second catalyst is a catalyst in which palladium is supported on a zirconia carrier. 6. Item 5. The method for purifying combustion exhaust gas according to any one of Items 1 to 4, wherein the second catalyst is a catalyst in which palladium and platinum are supported on a zirconia carrier. 7. The above items 1 to 6 in which the purification treatment is performed in a temperature range of 400 to 500 ° C.
The method for purifying combustion exhaust gas according to any one of the above. 8. In a device for purifying a flue gas containing an excessive amount of oxygen, a first catalyst that decomposes nitrogen oxides in the presence of methane is disposed upstream of the flue gas flow, and a second catalyst that oxidizes methane is disposed downstream. An apparatus for purifying combustion exhaust gas, comprising: 9. Item 9. The combustion exhaust gas purifying apparatus according to the above item 8, wherein a methane-containing gas injection device is arranged upstream of the first catalyst. 10. Item 8. The above-mentioned item 8, wherein the first catalyst is a catalyst in which palladium and platinum are supported on a sulfated zirconia carrier, and the second catalyst is a catalyst in which palladium is supported on a zirconia carrier.
Or a device for purifying combustion exhaust gas according to item 9.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the catalyst for reducing nitrogen oxides (first catalyst) used in the present invention, sulfate zirconia is used as a carrier (hereinafter sometimes referred to as "first carrier"). The sulfated zirconia is, for example, after immersing zirconium hydroxide in sulfuric acid and washing with water, or after impregnating zirconium hydroxide with an aqueous solution of ammonium sulfate, 450 g in air.
It is obtained by baking at about -700 ° C, more preferably about 500-600 ° C. If the firing temperature is too high, the sulfate groups may volatilize and disappear in large quantities,
If the temperature is too low, the effect of sintering will be insufficient, and a large amount of zirconium hydroxide will remain in the carrier, or the carrier will become amorphous, and stable sulfate zirconia will not be formed. During the sintering operation, it is inevitable that a part of the sulfate is volatilized. Therefore, it is necessary to provide an excessive amount of the sulfate corresponding to the volatile matter to the carrier finally obtained at the time of the above treatment or immersion. preferable.

The amount of sulfate (SO ₄ ²⁻ ) in the first carrier after calcination is usually about 0.5 to 20%, more preferably about 1 to 10%, based on the weight of zirconia. If the amount of sulfate is too small, the effect of using sulfate is not sufficiently exhibited, while if it is excessive, a stable sulfate zirconia carrier cannot be obtained.

Next, palladium and platinum are supported on the sulfated zirconia carrier obtained as described above. The loading method is not particularly limited as long as both components are loaded on the first carrier in a highly dispersed state, but is preferably carried out by impregnating the first carrier with an aqueous solution such as a nitrate or an ammine complex. The supported amounts of palladium and platinum (as Pd and Pt) are each about 0.05 to 2% based on the weight of sulfate-supported zirconia, more preferably
It should be about 0.1-1%. If the supported amount is too small, the activity becomes low, while if it is too high, these components are gathered to lose a highly dispersed state, and the desired effect cannot be obtained.

The ratio of palladium and platinum carried on the first carrier is usually about Pd: Pt = 1: 10 to 10: 1 by weight, more preferably about 4: 1 to 1: 4. is there.

Next, the sulfate-supported zirconia supporting the palladium component and the platinum component is dried and calcined in the air. The firing temperature is usually in the range of about 300 to 600 ° C, more preferably about 450 to 550 ° C. If the firing temperature is too low, the effect of the firing will be insufficient, while if it is too high, the specific surface area may decrease due to aggregation of palladium and platinum.

The first catalyst used in the present invention may be formed into an arbitrary shape such as a pellet according to a conventional method.
Alternatively, it may be used after being wash-coated on a refractory honeycomb carrier.

The methane oxidation catalyst (second catalyst) used in the present invention includes zirconia, sulfate zirconia,
Any of tungsten zirconia is used as a carrier (hereinafter sometimes referred to as “second carrier”).

The second carrier comprising sulfated zirconia is
What is necessary is just to manufacture like the said 1st support | carrier.

Tungsten zirconia is prepared by wet kneading amorphous zirconium oxide or zirconium hydroxide together with tungstic acid, and then drying the kneaded product to obtain 650-850.
It can be prepared by firing at a temperature of about ° C. The upper and lower limits of the firing temperature in this case are determined for the same reason as in the case of the nitrate zirconia described above. The amount of tungsten in the second carrier is usually about 2 to 20%, more preferably about 5 to 15%, based on the weight of zirconia. When the content of tungsten is too small, the effect of use is not sufficiently exhibited, whereas when the content is excessive, a stable tungsten zirconia support cannot be obtained.

The production of sulfated zirconia and tungsten zirconia can be confirmed by a known method such as a chemical method using a Hammett reagent or a crystallographic method by X-ray diffraction. For example, zirconia containing no sulfate or tungsten is mainly composed of monoclinic crystals, whereas sulfate zirconia and tungsten zirconia are mainly composed of tetragonal crystals. Can be easily confirmed. Sulfuric acid zirconia and tungsten zirconia are known materials (for example, “Surface”, Vol. 28, No. 7, page 481 (1990); “Surface”, Vol. 34, No. 2, page 51 (19)
96) etc.), SO ₄ / ZrO ₂ , W
O ₃ / ZrO ₂ or the like.

The second catalyst used in the present invention can be produced by supporting palladium or palladium and platinum as a catalytically active component on a second carrier, drying and calcining. The loading method is not particularly limited as long as the catalytically active component is loaded on the second carrier in a highly dispersed state, but preferably, the second carrier is a solution containing palladium ions or a solution containing palladium ions and platinum ions ( For example, it may be immersed in water or a mixture of water and acetone, ethanol, or the like in which a nitrate, an ammine complex, or the like is dissolved) and then dried.

Next, the dried product is placed in air at 450 to 700 ° C.
And more preferably at about 500 to 650 ° C. When the calcination temperature is too high, coarse particles are formed by the particle growth of the supported metal, whereas when it is too low, the particle growth proceeds during the use of the catalyst, and the catalyst activity becomes unstable. .

The amount of palladium carried on the second catalyst carrying palladium is usually about 1 to 25%, more preferably about 2 to 20%, based on the weight of the carrier. When the supported amount of palladium is too small, the catalytic activity is not sufficiently exhibited, whereas when it is too large, the particle size of palladium is increased and its specific surface area is reduced, so that palladium cannot be used effectively.

The amount of palladium supported on the second catalyst supporting palladium and platinum is the same as described above, and the amount of supported platinum is usually 5 to 100 parts by weight of palladium.
%, More preferably about 10 to 50%. When the supported amount of platinum is too small, the effect improvement by the combined use of platinum is not sufficiently achieved, whereas when it is too large,
The effect of palladium as a catalytically active component may be hindered.

The first and second catalysts according to the present invention can be formed into a desired shape according to a conventional method, depending on the use conditions and the like. For example, a known binder (zirconia sol or the like) may be added to the catalyst to form a pellet, or the surface of the refractory honeycomb substrate may be wash-coated. When wash-coating the surface of the refractory honeycomb substrate, the catalyst produced as described above may be wash-coated on the surface of the substrate in the form of a slurry, or the carrier may be previously wash-coated on the surface of the refractory honeycomb substrate, A predetermined catalytically active component may be supported by the above-described method.

The apparatus used in the purification of exhaust gas according to the present invention is, as shown in FIG. 1, a first catalyst for decomposing nitrogen oxides in the presence of methane using the first catalyst obtained above. It comprises a reactor 1 and a second reactor 2 for oxidizing methane using a second catalyst. If the amount of methane in the exhaust gas to be treated in the first reactor is too small, an injection device for adding methane or a methane-containing gas to the exhaust gas in advance is provided.

When the amount of the first catalyst used in the nitrogen oxide decomposition step (first step) is too small, sufficient nitrogen oxide removal cannot be achieved. Since the performance improvement corresponding to the usage cannot be obtained,
Economically disadvantaged. Accordingly, the first catalyst velocity space gas per time (GHSV) is at 15000H ^-1 or less, more preferably be used within the scope of the 1000~60000h ^-1.

The treatment temperature in the first step is usually from 350 to 550 ° C. in order to effectively utilize the high activity of the first catalyst.
Degree, more preferably about 400 to 500 ° C. If the treatment temperature in the first step is too low, the catalytic activity is not sufficiently exhibited, and the nitrogen oxide removing effect is not sufficiently achieved. On the other hand, if the processing temperature is too high, the durability of the catalyst is impaired.

The exhaust gas treated in the first step is
Next, it is sent to a methane oxidation step (second step). If the amount of the second catalyst used here is too small, the removal by methane oxidation is not performed well, whereas if it is too large, the methane conversion rate improves, but it is commensurate with the amount used. Because performance improvement cannot be obtained, it becomes economically disadvantageous,
Further, there is a problem that the pressure loss in the catalyst layer increases. Therefore, the second catalyst has a gas hourly space velocity (GHSV) of 500,000 h- ¹ or less, more preferably 2000 to 300.
It is desirable to use within the range of 000h ^-1 .

The processing temperature in the second step is usually from 300 to 700 to effectively utilize the good activity of the second catalyst.
C., more preferably about 400-600.degree. If the treatment temperature in the second step is too low, methane oxidation will not be sufficiently performed, whereas if the treatment temperature is too high, the durability of the catalyst will decrease.

In the present invention, since there is a region where the operating temperatures of the first catalyst and the second catalyst overlap, the first catalyst is placed upstream of a single catalyst container in accordance with the temperature of the exhaust gas. And the downstream side is filled with a second catalyst, so that exhaust gas treatment can be performed at the same temperature.

Alternatively, the processing temperature in the second step is controlled by filling both catalysts into separate catalyst containers, connecting the two containers by gas flow pipes, and appropriately adjusting the heat radiation from the flow pipes. Can also.

When carrying out the method of the present invention, if the amount of methane in the exhaust gas is smaller than the amount required for the reduction of nitrogen oxides, the methane injection device described above is used to supply methane such as methane or natural gas-based city gas. An appropriate amount of the contained gas can be added.

When the oxygen concentration in the exhaust gas is too low, an appropriate amount of air is mixed with the exhaust gas while paying attention so that the temperature of the exhaust gas in the second step does not become lower than the above-mentioned processing temperature. It can be brought into contact with a catalyst.

[0037]

According to the present invention, when treating an exhaust gas containing nitrogen oxides using methane as a reducing agent, the catalyst activity is stable over a long period of time even under the condition where an activity inhibiting factor such as water vapor or sulfur oxide is present. Is maintained, and a high conversion rate of methane is also maintained, so that the residual methane concentration in the treated gas can be kept low.

Although the combustion exhaust gas usually contains about 5 to 15% of water vapor, the method of the present invention can also treat such water vapor-containing exhaust gas.

Furthermore, the flue gas generally contains sulfur oxides, which are known to significantly reduce the catalytic activity. However, the two types of catalysts used in the method of the present invention are not capable of reducing the activity due to sulfur oxides. On the other hand, since it exhibits high resistance, a high degree of exhaust gas treatment effect is achieved.

Further, when unburned components such as carbon monoxide and aldehydes are contained in the flue gas, these can be oxidatively decomposed together with methane.

[0041]

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 1 125 g of zirconium hydroxide (Mitsuwa Chemical Co., Ltd.) was impregnated with 150 ml of an aqueous solution in which 25 g of ammonium sulfate was dissolved for 10 hours. After drying the impregnated body, it was calcined at 550 ° C. for 6 hours to obtain a sulfated zirconia support.

1.25 g of an aqueous solution of palladium nitrate containing 0.125 g of Pd and 2 g of an aqueous solution of tetraammineplatinum nitrate containing 6.3% by weight of Pt were mixed and stirred, and further mixed with pure water.
A solution diluted to 20 ml was prepared beforehand, impregnated with 25 g of the sulfated zirconia carrier obtained above for 15 hours, and dried. Next, the dried product was calcined at 500 ° C. for 9 hours to obtain a Pd—Pt / sulfate radical zirconia catalyst (first catalyst).

On the other hand, an aqueous solution of palladium nitrate containing 0.25 g of Pd and a solution of 0.083 g of dinitrodiammine platinum heated and dissolved in 1 ml of 69% nitric acid were mixed, and pure water was added to the mixture to give 20 ml.
Zirconia (Tosoh Corporation, "TZ-O")
5 g was impregnated at 0 ° C. for 15 hours. The product is then dried and 5
Pd-Pt / zirconia catalyst fired in air at 50 ° C for 2 hours
(Second catalyst) was obtained.

Fill the upstream side of the reaction tube with 4 ml of the first catalyst
The downstream side is filled with 1 ml of the second catalyst to form a catalyst layer
While maintaining the temperature inside the catalyst layer at 450 ° C,
ppm, methane 2000ppm, oxygen 10%, steam 9% and diacid
1 liter of combustion exhaust gas containing 3 ppm of sulfur
State). Nitrogen oxides after a predetermined time
(NO _x) And methane conversion are as shown in Table 1.
Was.

[Table 1]

Here, the conversion (%) of NO _x and methane is
It means the value calculated by the following formula.

NO _x conversion rate (%) = {1− (NO _xout / NO _xin )} × 100 CH ₄ conversion rate (%) = CO _2out / (CH _4out + CO _2out ) × 100 where NO _xout is a reaction shows the concentration of NO _x tube outlet, NO _xin indicates the concentration of NO _x inlet reaction tube, CO _2out represents a carbon dioxide concentration of the reaction tube outlet, CH _4out shows the methane concentration of the catalyst layer outlet.

From the results shown in Table 1, it is clear that even when the gas to be treated contains water vapor and sulfur oxides, stable and good nitrogen oxide removing effect and methane oxidation effect are achieved. is there. Example 2 A tubular exhaust gas purifier made of stainless steel (Example 1
4 ml of the first catalyst and 1 ml of the second catalyst obtained in the above are sequentially filled in the exhaust gas flow direction to form a catalyst layer), while maintaining the catalyst layer outlet temperature at 450 ° C. A flue gas containing 150 ppm of nitrogen monoxide, 2000 ppm of methane, 10% of oxygen, 9% of steam and 3 ppm of sulfur dioxide was circulated. Gas hourly space velocity (GHSV) is 1500 at the first catalyst layer
A 0h ^-1, it was 60000H ^-1 in the second catalyst layer.
The nitrogen oxide removal rate 200 hours after the start of the reaction was 45%, and the methane concentration at the outlet of the catalyst layer was 200 ppm. Example 3 The same zirconia carrier as that of Example 1 (manufactured by Tosoh Corporation, "T
ZO ″) 5 g of Pd was impregnated with 20 ml of an aqueous palladium nitrate solution containing 0.25 g at 0 ° C. for 15 hours, and then dried,
Calcination in air at ℃ ° C for 2 hours gave a Pd / zirconia catalyst (second catalyst).

Next, the Pd-Pt / Pd / Pt /
Example 1 Using 4 ml of sulfated zirconia catalyst as the first catalyst and 1 ml of the Pd / zirconia catalyst obtained above as the second catalyst
The combustion exhaust gas was treated under the same conditions as described above. The conversion rates of nitrogen oxides (NO _x ) and methane after the lapse of a predetermined time were as shown in Table 2.

[Table 2]

From the results shown in Table 2, Pd was used as the second catalyst.
It is clear that a stable and good nitrogen oxide removing effect and a methane oxidizing effect are achieved even when the / zirconia catalyst is used.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an outline of a method of the present invention and an apparatus used in the method of the present invention.

[Explanation of symbols]

 1. Nitrogen oxide decomposition apparatus (first step) 2. Methane oxidation apparatus (second step) 3. Methane or methane-containing gas injection apparatus

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takanori Nakahira Inventor, Osaka Gas Co., Ltd. 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka (72) Inventor Masataka Masuda Hirano-cho, Chuo-ku, Osaka-shi, Osaka 4-1-2, Osaka Gas Co., Ltd. (72) Inventor Takenori Hirano 1385-2 Kamisababuchi, Izumi-shi, Kagoshima F-term in Kyushu Catalyst Research Co., Ltd. 4D048 AA06 AA18 AB01 AB02 AC09 BA08X BA27Y BA30X BA31X BA39X BA41X BA42X BA46X BB01 BB02 BD01 CC32 CC39 CC47 CC52 DA03 DA06 4G069 AA01 AA03 BA05A BA05B BB10A BB10B BC51A BC51B BC72A BC72B BC75A BC75B CA02 CA07 CA10 CA13 CA15 DA06 EA01Y

Claims (10)

[Claims] 1. A method for purifying a combustion exhaust gas containing an excessive amount of oxygen, wherein a first catalyst for decomposing nitrogen oxides in the presence of methane and a second catalyst for oxidizing methane are used. Purification method of combustion exhaust gas. 2. The method according to claim 1, wherein the combustion exhaust gas is a natural gas combustion exhaust gas. 3. The method according to claim 1, wherein methane is added to the flue gas prior to contacting the flue gas with the first catalyst.
The method for purifying combustion exhaust gas according to item 1. 4. The catalyst according to claim 1, wherein the first catalyst is a catalyst in which palladium and platinum are supported on a sulfated zirconia carrier.
The method for purifying combustion exhaust gas according to any one of the above. 5. The method for purifying combustion exhaust gas according to claim 1, wherein the second catalyst is a catalyst in which palladium is supported on a zirconia carrier. 6. The method for purifying combustion exhaust gas according to claim 1, wherein the second catalyst is a catalyst in which palladium and platinum are supported on a zirconia carrier. 7. The method for purifying combustion exhaust gas according to claim 1, wherein the purification treatment is performed in a temperature range of 400 to 500 ° C. 8. An apparatus for purifying a flue gas containing an excessive amount of oxygen, wherein a first catalyst for decomposing nitrogen oxides in the presence of methane is arranged upstream of the flue gas stream, and methane is oxidized downstream. An apparatus for purifying combustion exhaust gas, wherein a second catalyst is disposed. 9. The exhaust gas purifying apparatus according to claim 8, wherein a methane-containing gas injection device is arranged upstream of the first catalyst. 10. The catalyst according to claim 8, wherein the first catalyst is a catalyst in which palladium and platinum are supported on a sulfated zirconia carrier, and the second catalyst is a catalyst in which palladium is supported on a zirconia carrier. Of combustion exhaust gas.