JP2011194316A - Catalyst and method for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst which exhibits high ability to crack methane even at low temperature when the catalyst is used for oxidatively removing methane in combustion exhaust gas including methane, sulfur oxides and excessive oxygen, and to provide a method for oxidatively removing methane in the exhaust gas by using the catalyst.SOLUTION: The catalyst is used for oxidatively removing methane in the combustion exhaust gas including methane, sulfur oxides and excessive oxygen, and is obtained by depositing platinum, iridium and zirconium on a titanium oxide carrier. The method for oxidatively removing methane in the combustion exhaust gas including methane, sulfur oxides and excessive oxygen comprises a step of bringing the exhaust gas into contact with the catalyst at 300-450°C.

Description

  The present invention relates to a catalyst for oxidation removal of methane in combustion exhaust gas containing methane, sulfur oxides and excess oxygen, and a method for oxidation removal.

  In the present specification, “containing excess oxygen” means that the gas to be treated (combustion exhaust gas) brought into contact with the catalyst of the present invention completely oxidizes reducing components such as hydrocarbons and carbon monoxide contained therein. It means that an oxidizing component such as oxygen and nitrogen oxide is contained in an amount more than that required for the purpose.

  As a catalyst for removing oxidation of hydrocarbons in exhaust gas, it is known that a catalyst supporting a platinum group metal such as platinum or palladium exhibits high performance. For example, an exhaust gas purifying catalyst having platinum and palladium supported on an alumina carrier is disclosed (see Patent Document 1). However, even if such a catalyst is used, methane has high chemical stability when the main component of hydrocarbons in the exhaust gas is methane, such as methane fermentation gas or natural gas combustion exhaust gas. In addition, there is a problem that sufficient methane removal is not achieved.

  In addition, since combustion exhaust gas necessarily contains reaction inhibitory substances such as sulfur oxides (SOx) derived from sulfur compounds contained in the fuel, reaction inhibitory substances must be deposited on the catalyst surface. Therefore, it is unavoidable that the catalyst activity significantly decreases with time.

  For example, Lampert et al. (Lampert et al.) Show that when methane oxidation is carried out using a palladium catalyst, only 0.1 ppm of sulfur dioxide is present and its catalytic activity is almost lost within a few hours. It has been clarified that the presence of sulfur oxide has a significant adverse effect on the catalytic activity (see Non-Patent Document 1).

  Furthermore, 7 g / l or more of palladium and 3 to 20 g / l of platinum were supported on the honeycomb substrate via an alumina carrier as a catalyst for oxidizing low-concentration hydrocarbons contained in the exhaust gas in which an excessive amount of oxygen was present. A catalyst is also disclosed (see Patent Document 2). However, even when this catalyst is used, durability over a long period is not sufficient, and deterioration of the catalyst activity over time is inevitable under the condition where sulfur oxides coexist.

  Thus, the big problem of the prior art is that a high removal rate cannot be obtained with respect to methane, and further, the removal rate is greatly reduced under the condition where sulfur oxides coexist.

  In view of such a situation, it is disclosed that a catalyst in which palladium or palladium and platinum are supported on a zirconium oxide support continues to maintain high methane oxidation activity even in the presence of sulfur oxide (see Patent Document 3). ). However, since this catalyst has a low methane oxidation activity particularly in a low temperature range of about 400 ° C. or less, a large amount of catalyst is required to ensure sufficient performance at a low temperature.

  In addition, an unburned hydrocarbon oxidation catalyst in exhaust gas in which platinum and palladium are supported on a titanium oxide support has been proposed (see Patent Document 4), but this catalyst is also particularly in a low temperature range of about 400 ° C. or lower. Methane oxidation activity is not enough.

  While it was theorized that palladium is effective for the oxidation of methane (see Non-Patent Document 2 and Non-Patent Document 3), it does not contain palladium and only platinum is supported on a support made of tin oxide. There is also a document showing that the catalyst is active in removing methane from combustion exhaust gas by oxidation (see Patent Document 5). However, this catalyst does not have sufficient methane removal performance at 400 ° C. or lower, and requires a large amount of expensive platinum.

A catalyst for purifying hydrocarbons in combustion exhaust gas containing methane and containing oxygen excessively, comprising zirconium oxide supporting at least one selected from the group consisting of platinum, palladium, rhodium and ruthenium and iridium. It is also disclosed that a catalyst having a specific surface area of ² to 60 m ² / g continues to maintain high methane oxidation activity even at a low temperature of about 400 ° C. in the presence of sulfur oxide (patent document) 6). However, this catalyst has a practical problem in that it requires a relatively large amount of iridium, which is a very rare noble metal.

  Also proposed is a catalyst for oxidizing and removing methane in combustion exhaust gas containing sulfur oxide in a low temperature region, in which iridium is supported as a promoter on a catalyst in which platinum is supported on tin oxide (see Patent Document 7). However, this catalyst does not have sufficient methane removal performance below 400 ° C.

  Also proposed is a catalyst for oxidizing and removing methane in combustion exhaust gas containing methane, sulfur oxides and excess oxygen, wherein platinum and iridium are supported on a titanium oxide carrier (see Patent Document 8). Yes. This catalyst exhibits high methane oxidation activity even at a low temperature, and its activity decrease due to the coexistence of sulfur compounds is small, but further performance improvement is required. For this reason, addition of antimony and niobium (see Patent Document 9) has also been proposed, but there are difficulties in handling antimony and niobium, and problems remain in practice.

  In addition, in order to decompose and remove NOx components contained in the combustion exhaust gas of gas fuel, a porous carrier made of one or more of alumina, zirconium oxide, and titanium oxide is used with one or more of iridium, platinum, and rhodium. A catalyst for removing NOx carrying a plurality of species has been proposed (see Patent Document 10). However, this document only shows NOx removal performance, and does not teach any removal rate of hydrocarbons. What is the possibility of oxidative decomposition of the most difficult-to-decompose methane among hydrocarbons? I did not suggest.

  A method for producing an exhaust gas purifying catalyst in which at least one of platinum and rhodium and at least one of iridium and ruthenium are supported on an inorganic support such as activated alumina by a specific method using citric acid. Is disclosed (see Patent Document 11). According to this document, iridium and / or ruthenium form a solid solution having a high melting point with platinum and / or rhodium, so that the heat resistance of the obtained catalyst is improved. However, this document only shows that the NOx conversion rate of the obtained catalyst has been improved, and does not teach any oxidative decomposition of methane, which is particularly difficult to decompose among the hydrocarbons contained in the exhaust gas. .

  There has been proposed a lean burn engine exhaust gas denitration catalyst in which iridium is supported on various supports such as alumina, silica, zirconium oxide, and titanium oxide (see Patent Document 12). However, this document also does not show recognition that methane is particularly difficult to decompose among various hydrocarbons present in the exhaust gas. Therefore, it has not been clarified at all about how methane can be efficiently oxidized and decomposed.

Japanese Patent Laid-Open No. 51-106691 JP-A-8-332392 JP-A-11-319559 JP 2000-254500 A Japanese Patent Laid-Open No. 2004-351236 International Publication WO2002 / 040152 JP 2006-272079 A JP 2008-246473 A JP 2009-262131 A Japanese Patent Laid-Open No. 3-293035 Japanese Patent Laid-Open No. 3-98644 Japanese Unexamined Patent Publication No. 7-80315

Applied Catalysis B: Environmental, Vol. 14, 1997, p.211-223 Industrial and Engineering Chemistry, Vol. 53, 1961, p.809-812 Industrial and Engineering Chemistry Product Research and Development, Volume 19, 1980, p.293-298

  An object of the present invention is to provide a catalyst that exhibits high methane resolution even at low temperatures in the oxidation removal of methane in combustion exhaust gas containing methane, sulfur oxides, and excess oxygen, and methane in exhaust gas using this catalyst. It is to provide an oxidation removal method.

The present invention provides an exhaust gas purification catalyst and an exhaust gas purification method as described below.
Item 1. A catalyst for oxidizing and removing methane in combustion exhaust gas containing methane, sulfur oxides and excess oxygen, wherein platinum, iridium and zirconium are supported on a titanium oxide support.
Item 2. A method for oxidizing and removing methane in a combustion exhaust gas containing methane, sulfur oxides and excess oxygen, wherein the combustion exhaust gas is contacted with the catalyst according to claim 1 at a temperature of 300 to 450 ° C.

  Hereinafter, the present invention will be described in detail.

  The catalyst of the present invention is a catalyst for oxidizing and removing methane in combustion exhaust gas, and is characterized in that zirconium is supported on titanium oxide as a carrier together with platinum and iridium as catalytic active components.

  In the preparation of the catalyst of the present invention, when zirconium, platinum and iridium are supported on titanium oxide, each component may be sequentially supported, or a plurality of components may be simultaneously supported. Zirconium is supported on a titanium oxide precursor such as titanium oxide or hydrous titanium oxide, and after firing, platinum and iridium are supported.

  Hereinafter, this case will be described in detail.

  When the surface area of titanium oxide as a support is too small, the catalytically active component cannot be kept highly dispersed. On the other hand, when the surface area is too large, the thermal stability of the titanium oxide is not sufficient, and the titanium oxide itself may be sintered during the use of the catalyst.

The specific surface area of titanium oxide (referred to herein as the specific surface area by the BET method) is usually about ^{2 to} 150 m ² / g, preferably about 50 to 90 m ² / g. The crystal form of titanium oxide is preferably anatase type, but may contain 25% or less of rutile type titanium oxide on a mass basis. A known method such as X-ray diffraction measurement can be applied to the measurement of the crystal phase content ratio. Such a titanium oxide may be a commercially available titanium oxide for a catalyst carrier, or may be prepared by a method such as firing at 300 ° C. to 500 ° C. in an oxidizing atmosphere such as air.

The supported amount of zirconium is preferably about 0.1 to 10%, more preferably about 0.5 to 2% in terms of mass ratio with respect to titanium oxide as ZrO ₂ .

  Zirconium support can be obtained by impregnating the above-mentioned titanium oxide or titanium oxide precursor with an aqueous solution of a zirconium compound, drying, and firing. As the zirconium compound, water-soluble zirconium compounds such as zirconyl oxychloride, zirconyl oxynitrate, and zirconium sulfate can be used.

  After impregnating with zirconium, drying and firing are performed to obtain titanium oxide supporting zirconium. Firing may be performed under air circulation. Or you may carry out in distribution | circulation of oxidizing gas, such as the gas which mixed air or oxygen, and inert gas, such as nitrogen, suitably.

  If the firing temperature is too high, the grain growth of titanium oxide proceeds and the platinum and iridium described later cannot be supported in a highly dispersed state. On the other hand, if it is too low, the calcination is not performed sufficiently, so that sintering of zirconium or titanium oxide proceeds during use of the catalyst, and there is a possibility that stable activity cannot be obtained. Therefore, in order to stably obtain high catalytic activity, the calcination temperature is preferably about 600 to 800 ° C, more preferably about 650 to 750 ° C.

  The firing time is not particularly limited, but is usually about 1 to 50 hours, preferably about 3 to 20 hours.

Although not necessarily clear the presence state of the zirconium in this catalyst, believed to be present in the form of oxide as ZrO _2, either present as minute ZrO ₂ crystals, at least a portion of titanium oxide There is also a possibility that it is in solid solution.

  The catalyst carrier may contain a small amount of components other than titanium oxide such as alumina and silica in order to improve adhesion to a support such as cordierite and sinterability, but these components are based on mass. It is desirable not to exceed 2%.

  When the amount of platinum and iridium supported on titanium oxide is too small, the catalytic activity is low, whereas when it is too large, the particle size becomes large and the supported catalytically active component is not effectively used.

  The supported amount of platinum is preferably about 0.5 to 20% by mass ratio with respect to titanium oxide, and more preferably about 0.5 to 5%. The supported amount of iridium is preferably about 0.5 to 20% by mass ratio with respect to titanium oxide, and more preferably about 0.5 to 5%. The ratio of the supported amount of platinum and iridium is preferably about 0.2 to 5 and more preferably about 0.4 to 2 in terms of mass ratio of Pt / Ir.

  The catalyst of the present invention is obtained, for example, by impregnating a mixed aqueous solution of a platinum compound and an iridium compound with titanium oxide supporting zirconium prepared as described above, drying, and firing.

  The impregnation operation may be performed using an aqueous solution prepared by dissolving a water-soluble compound such as a chloro complex, an ammine complex, or a nitrate in pure water, or an organic metal compound such as an acetylacetonato complex may be organically mixed with acetone or the like You may carry out using the organic-solvent solution melt | dissolved in the solvent.

  Examples of the water-soluble compound include chloroiridate (hexachloroiridate), hexaammineiridium nitrate, chloroplatinic acid, tetraammineplatinum nitrate, and dinitrodiammineplatinum. If the solubility is low and the desired concentration cannot be obtained by dissolving in pure water, dilute nitric acid, dilute hydrochloric acid, or aqueous ammonia may be added to increase the solubility.

  Examples of the organometallic compound include tris (acetylacetonato) iridium and bis (acetylacetonato) platinum.

  The loading of iridium and platinum may be performed sequentially as necessary, and in that case, a drying or firing step may be interposed between the respective loadings as necessary.

  The impregnation time is not particularly limited as long as a predetermined loading amount is ensured, but is usually about 1 to 50 hours, preferably about 3 to 20 hours.

  Next, the titanium oxide supporting a predetermined metal component is evaporated or dried or dried as necessary, and then fired.

  Firing may be performed under air circulation. Or you may carry out in distribution | circulation of oxidizing gas, such as the gas which mixed air or oxygen, and inert gas, such as nitrogen, suitably.

  If the firing temperature is too high, grain growth of the supported metal proceeds and high activity cannot be obtained. On the other hand, if it is too low, the calcination is not performed sufficiently, so that the metal particles supported during the use of the catalyst may become coarse and stable activity may not be obtained. Therefore, in order to stably obtain high catalytic activity, the calcination temperature is preferably about 450 to 650 ° C, more preferably about 500 to 600 ° C.

  The firing time is not particularly limited, but is usually about 1 to 50 hours, preferably about 3 to 20 hours.

  The catalyst of the present invention may be used after being molded into an arbitrary shape such as pellets or honeycombs, or may be used by wash coating on a refractory honeycomb. Preferably, the refractory honeycomb is wash coated.

  When wash-coating on a fire-resistant honeycomb, the catalyst prepared by the above-mentioned method may be slurry-coated and washed, or after the titanium oxide is washed on the fire-resistant honeycomb in advance, the impregnation described above may be performed. The active ingredient may be supported according to the technique. In either case, a binder can be added as necessary. As a preferred example, a slurry is prepared by adding a binder (e.g., titanium oxide sol), zirconium oxynitrate, an appropriate amount of water, and a thickener as necessary to a titanium oxide support, and coating this on a fire-resistant honeycomb, A method of forming a titanium oxide layer supporting zirconium on a refractory honeycomb by firing at 650 to 750 ° C. after drying and impregnating and supporting iridium and platinum is included in this.

The specific surface area of the catalyst of the present invention is usually about ^{2 to} 90 m ² / g, preferably about ²⁰ to 60 m ² / g. If the specific surface area of the catalyst exceeds 90 m ² / g, the durability of the catalyst may be lowered due to the progress of sintering of the support during use. On the other hand, if it is less than 2 m ² / g, there is a possibility that the active metal dispersion is lowered and sufficient activity cannot be obtained.

  The exhaust gas purification method of the present invention is a treatment target for combustion exhaust gas containing methane, sulfur oxides, and excess oxygen. In addition to methane, the combustion exhaust gas may contain lower hydrocarbons such as ethane and propane, carbon monoxide, and oxygen-containing combustible components. Since these are easily decomposable as compared with methane, they can be easily oxidized and removed simultaneously with methane by the method of the present invention.

  The concentration of flammable components in the exhaust gas is not particularly limited, but if it is too high, an extreme temperature rise occurs in the catalyst layer, which may adversely affect the durability of the catalyst. The following is preferable.

  The method for oxidizing and removing methane in exhaust gas according to the present invention is characterized by using the catalyst obtained as described above.

When the amount of the catalyst used is too small, an effective purification rate cannot be obtained. Therefore, it is preferable to use an amount that gives a space velocity per gas hour (GHSV) of 200,000 h ⁻¹ or less. On the other hand, the lower the gas hourly space velocity (GHSV), the greater the amount of catalyst, so the purification rate improves, but if GHSV is too low, it is economically disadvantageous and pressure loss in the catalyst layer Becomes larger. Therefore, the lower limit of GHSV may preferably be about 1,000 h ^-1, and more preferably about 5,000h ^-1.

  The oxygen concentration in the exhaust gas, which is the gas to be treated, is not particularly limited as long as it contains oxygen in excess. It is preferred that there be about 5 times or more (more preferably about 10 times or more) of oxygen equivalent to the oxidation equivalent of the components.

  When the oxygen concentration in the exhaust gas is extremely low, the reaction rate may decrease. Therefore, a required amount of air, excess oxygen exhaust gas, or the like may be mixed in advance.

  The catalyst for removing oxidation of methane in the exhaust gas of the present invention has high activity. However, when the exhaust gas treatment temperature is too low, the activity is lowered and a desired methane conversion rate cannot be obtained. On the other hand, when the treatment temperature is too high, the durability of the catalyst may deteriorate.

  The temperature of the catalyst layer is usually about 300 to 500 ° C, preferably about 300 to 450 ° C.

  In addition, when the concentration of hydrocarbons in the gas to be treated is extremely high, a rapid reaction occurs in the catalyst layer, which adversely affects the durability of the catalyst, so the temperature rise in the catalyst layer is usually about 150 ° C. or less, It is preferable to use it under conditions of about 100 ° C. or less.

  The combustion exhaust gas normally contains about 5 to 15% of water vapor, but according to the present invention, effective methane oxidation removal is achieved even for the exhaust gas containing water vapor.

  The combustion exhaust gas usually contains sulfur oxides that significantly reduce the catalyst activity. However, the catalyst of the present invention exhibits a particularly high resistance to the activity reduction caused by sulfur oxides, so that 0.1% by volume. Even when about 30 ppm of sulfur oxide is contained, the methane conversion is not substantially affected.

  According to the present invention, it becomes possible to stably oxidize and remove methane in combustion exhaust gas, so that it contains sulfur oxides such as combustion exhaust gas such as methane fermentation gas and natural gas city gas, and various process gases. By treating the exhaust gas to be treated by the method of the present invention, methane contained in the exhaust gas is oxidized and removed, and the reaction heat can be recovered and effectively used as energy, and also contributes to the improvement of the global environment.

  Since the catalyst of the present invention exhibits very excellent resistance to activity inhibition by water vapor and sulfur oxides, even in exhaust gas containing a large amount of water vapor and containing sulfur oxide like combustion exhaust gas, high methane Exhibits oxidative activity.

  Further, since the catalyst of the present invention exhibits high activity even at a low temperature, the amount of expensive noble metal used can be reduced and the economy is excellent.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated in detail, this invention is not limited to these Examples.

Example 1 (Preparation of 2% Pt-4% Ir / 0.68% ZrO ₂ / Titanium Oxide Catalyst)
Zirconyl oxynitrate dihydrate (ZrO (NO ₃ ) ₂ · 2H ₂ O) 0.66 g was dissolved in 80 g of pure water. This solution was impregnated in 45 g of titanium oxide (“MC-90” manufactured by Ishihara Sangyo Co., Ltd., specific surface area 82 m ² / g). After evaporating to dryness, it was calcined in air at 700 ° C. for 6 hours to obtain 0.68% ZrO ₂ / titanium oxide (specific surface area 43 m ² / g).

In distilled water (15 ml), an aqueous solution of hexachloroplatinic acid (H ₂ PtCl ₆ ) containing 1.6.3% by mass as Pt (1.84 g) and an aqueous solution of hexachloroiridate (H ₂ IrCl ₆ ) containing 8.7% by mass as Ir (6.9 g) was added and the solution was impregnated with 15 g of the above 0.68% ZrO ₂ / titanium oxide. After evaporating to dryness and drying at 120 ° C., the mixture was calcined in air at 550 ° C. for 6 hours to obtain a 2% Pt-4% Ir / 0.68% ZrO ₂ / titanium oxide catalyst. The specific surface area of this catalyst was 42 m ² / g.

Example 2 (Preparation of 2% Pt-4% Ir / 1.35% ZrO ₂ / titanium oxide catalyst)
2% Pt-4% Ir / 1.35% ZrO ₂ / titanium oxide catalyst as in Example 1 except that 1.32 g of zirconyl oxynitrate dihydrate (ZrO (NO ₃ ) ₂ · 2H ₂ O) was used Got. BET specific surface area of 1.35% ZrO ₂ / titanium oxide and 2% Pt-4% Ir / 1.35% ZrO 2 / titanium oxide catalyst were respectively 46m ² / g and 45 m ² / g.

Example 3 (Preparation of 2% Pt-4% Ir / 2.7% ZrO ₂ / titanium oxide catalyst)
2% Pt-4% Ir / 2.7% ZrO ₂ / titanium oxide catalyst as in Example 1 except that 2.64 g of zirconyl oxynitrate dihydrate (ZrO (NO ₃ ) ₂ · 2H ₂ O) was used Got. BET specific surface area of 2.7% ZrO ₂ / titanium oxide and 2% Pt-4% Ir / 2.7% ZrO 2 / titanium oxide catalyst were respectively 46m ² / g and 44m ² / g.

Comparative Example 1 (Preparation of 2% Pt-4% Ir / titanium oxide catalyst)
Titanium oxide (“MC-50” manufactured by Ishihara Sangyo Co., Ltd., specific surface area 62 m ² / g) was calcined in air at 700 ° C. for 6 hours to obtain calcined titanium oxide (specific surface area 32 m ² / g). A 2% Pt-4% Ir / titanium oxide catalyst was obtained in the same manner as in Example 1 except that this calcined titanium oxide was used instead of 0.68% ZrO ₂ / titanium oxide. The specific surface area of this catalyst was 32 m ² / g.

Comparative Example 2 (Preparation of 2% Pt-4% Ir / titanium oxide catalyst (2))
Titanium oxide (“MC-90” manufactured by Ishihara Sangyo Co., Ltd., specific surface area 82 m ² / g) was calcined in air at 700 ° C. for 6 hours to obtain calcined titanium oxide (specific surface area 35 m ² / g). A 2% Pt-4% Ir / titanium oxide catalyst (2) was obtained in the same manner as in Example 1 except that this calcined titanium oxide was used instead of 0.68% ZrO ₂ / titanium oxide. The specific surface area of this catalyst was 35 m ² / g.

Comparative Example 3 (Preparation of 2% Pt-4% Ir / zirconium oxide catalyst)
Zirconium oxide (“N-PC” manufactured by Nippon Electric Works Co., Ltd., specific surface area 28 m ² / g) was calcined in air at 700 ° C. for 6 hours to obtain calcined zirconium oxide (specific surface area 19 m ² / g). A 2% Pt-4% Ir / zirconium oxide catalyst was obtained in the same manner as in Example 1 except that this calcined zirconium oxide was used instead of 0.68% ZrO ₂ / titanium oxide. The specific surface area of this catalyst was 19 m ² / g.

Comparative Example 4 (Preparation of 2% Pt-4% Ir / 1.7% TiO ₂ / zirconium oxide catalyst)
2.18 g of titanium sulfate (Ti (SO ₄ ) ₂ · 6H ₂ O) was dissolved in 30 g of pure water. This solution was impregnated with 30 g of zirconium oxide (“N-PC” manufactured by Nippon Electric Works Co., Ltd., specific surface area 28 m ² / g). After evaporating to dryness, it was calcined at 700 ° C. in air for 6 hours to obtain 1.7% TiO ₂ / zirconium oxide (specific surface area 25 m ² / g). A 2% Pt-4% Ir / 1.7% TiO ₂ / zirconium oxide catalyst was obtained in the same manner as in Example 1 except that this 1.7% TiO ₂ / zirconium oxide was used instead of 0.68% ZrO ₂ / titanium oxide. . The specific surface area of this catalyst was 25 m ² / g.

Comparative Example 5 (Preparation of 2% Pt-4% Ir / zirconium oxide + titanium oxide catalyst)
Instead of 0.68% ZrO ₂ / titanium oxide, zirconium oxide (“N-PC” manufactured by Nippon Electric Works) and titanium oxide (“MC-50” manufactured by Ishihara Sangyo Co., Ltd.) fired in air at 700 ° C. for 6 hours. 2% Pt-4% Ir / zirconium oxide + titanium oxide catalyst was obtained in the same manner as in Example 1 except that a mixture of the above in a mass ratio of 1: 2 was used. The specific surface area of this catalyst was 25 m ² / g.

[Activity evaluation test]
Each of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was subjected to tableting, and then 1.45 g (1.5 to 2.4 ml) of each molded body was filled in a quartz reaction tube (inner diameter 14 mm). Next, a gas having a composition consisting of 1,000 ppm of methane, 10% oxygen, 10% water vapor (volume basis) and the balance nitrogen is circulated through the reaction tube at a flow rate of 2 liters / minute (volume in the standard state) to form a catalyst. The methane conversion at the layer temperatures of 375 ° C. and 450 ° C. was measured (initial conversion). The gas composition before and after the reaction layer was measured by a gas chromatograph having a flame ionization detector and a thermal conductivity detector. Then, with the catalyst layer temperature maintained at 450 ° C, the reaction was continued by adding 3 ppm of sulfur dioxide to the reaction gas, and methane conversion was performed at catalyst layer temperatures of 375 ° C and 450 ° C at 20 and 60 hours, respectively. The rate was measured similarly. Under any catalyst / reaction condition, the production of carbon dioxide corresponding to the decrease in methane concentration was confirmed, and methane was completely oxidized on the catalyst.

Table 1 shows the measurement results of methane conversion (%). Here, the methane conversion is a value obtained by the following equation.
CH ₄ conversion (%) = 100 × (1-CH ₄ -OUT / CH ₄ -in)
In the formula, “CH ₄ -OUT” indicates the methane concentration at the catalyst layer outlet, and “CH ₄ -in” indicates the methane concentration at the catalyst layer inlet.

  As can be seen from the fact that the methane removal rate of 95% or more is obtained at 375 ° C., the catalysts of Examples 1 to 3 show a high initial activity, and the decrease in activity due to the coexistence of SOx is small. However, the methane removal rate of 80% or more was maintained. At 450 ° C., the methane removal rate was 100% both at the initial stage and 60 hours after the introduction of SOx. It is clear that the catalyst of the present invention is superior to the catalyst containing no zirconium (Comparative Examples 1 and 2).

In addition, even if the combination of zirconium and titanium is common, when the titanium is supported on the ZrO ₂ carrier (Comparative Example 4) or when the carrier is simply a mixture of ZrO ₂ and TiO ₂ , It is clear that the same effect as the invention cannot be obtained.

Claims (2)

  A catalyst for oxidizing and removing methane in combustion exhaust gas containing methane, sulfur oxides and excess oxygen, wherein platinum, iridium and zirconium are supported on a titanium oxide support.   A method for oxidizing and removing methane in a combustion exhaust gas containing methane, sulfur oxides and excess oxygen, wherein the combustion exhaust gas is contacted with the catalyst according to claim 1 at a temperature of 300 to 450 ° C.