JP6771330B2 - Method for manufacturing catalyst for removing methane oxidation and method for removing methane oxidation - Google Patents

Description

The present invention relates to a method for producing a catalyst for removing methane oxidation and a method for removing methane oxidation for oxidizing and removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen.
In the present specification, "containing excess oxygen" means that the gas to be treated, which is brought into contact with the catalyst for removing methane oxidation, completely oxidizes the reducing components such as hydrocarbons and carbon monoxide contained therein. It means that it contains more oxidizing components such as oxygen and nitrogen oxides than necessary.
That is, the gas to be treated containing excess oxygen means a gas to be treated having an oxygen concentration containing excess oxygen than the oxidation equivalent of the reducing component in the gas to be treated.

It is known that a catalyst supporting a platinum group metal such as platinum or palladium exhibits high performance as a hydrocarbon oxidation removal catalyst. For example, an exhaust gas purification catalyst in which platinum and palladium are supported on an alumina carrier is disclosed (see Patent Document 1). However, even if such a catalyst is used, when the main component of the hydrocarbon contained is methane, such as the combustion exhaust gas of methane fermentation gas or natural gas, methane has high chemical stability. , There is a problem that sufficient methane removal is not achieved.

Further, when the gas to be treated is combustion exhaust gas, a reaction inhibitor such as sulfur oxide (SOx) derived from a sulfur compound contained in the fuel is inevitably contained, so that the catalyst surface inevitably contains a reaction inhibitor. It is inevitable that the catalytic activity will be significantly reduced over time due to the precipitation of the reaction inhibitor.

For example, Lampert et al. (Lampert et al.), When methane oxidation is performed using a palladium catalyst, the presence of only 0.1 ppm of sulfur dioxide causes almost no catalytic activity to be lost within a few hours. It has been clarified that the presence of sulfur oxides has a significant adverse effect on catalytic activity (see Non-Patent Document 1).

As a catalyst for oxidizing low-concentration hydrocarbons contained in exhaust gas containing an excess amount of oxygen, a catalyst in which 7 g / L or more of palladium and 3 to 20 g / L of platinum are supported on a honeycomb substrate via an alumina carrier is also available. It has been proposed (see Patent Document 2). However, even if this catalyst is used, its long-term durability is not sufficient, and under the condition that sulfur oxides coexist, deterioration of the catalytic activity over time is unavoidable.

In recent years, the problem of global warming has become strongly recognized, and the problem is that a large amount of gas containing dilute (about 0.1 to 1%) methane, such as coal mine ventilation gas, is released. It is regarded as an issue, and its economic processing is also an issue. Here, too, a highly active catalyst that can be treated at the lowest possible temperature is required for removing methane by catalytic oxidation. In addition to methane, coal mine ventilation gas may contain sulfur compounds (hydrogen sulfide, mercaptan, sulfur dioxide) derived from coal components, and hydrogen sulfide and mercaptan are oxidized on the catalyst to oxidize sulfur. Since it changes into a substance, the activity decreases due to poisoning as in the case of combustion exhaust gas.

Therefore, the major problems of the prior art are that a high removal rate for methane cannot be obtained, and that the removal rate is significantly reduced under the condition that the sulfur compound coexists.

In view of such circumstances, it is disclosed that a catalyst in which palladium or palladium and platinum are supported on a zirconium oxide carrier continues to maintain high methane oxidation activity even in the presence of sulfur oxides (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 lower, a large amount of catalyst is required to ensure sufficient performance at a low temperature.

A catalyst for purifying hydrocarbons in combustion exhaust gas containing methane and excessive oxygen, in which zirconium oxide is supported with at least one selected from the group consisting of platinum, palladium, rhodium and ruthenium and iridium. It is 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 a sulfur oxide (Patent). Reference 4).

It is widely known today that a catalyst in which iridium and platinum are supported on a zirconium oxide carrier exhibits high methane oxidation activity in the presence of sulfur oxides (for example, Patent Document 5 and Non-Patent Documents). 2 etc.), but there is a need for a catalyst that can obtain higher methane oxidation activity even at low temperatures.

Patent Document 6 discloses a catalyst for oxidizing and removing methane in a gas to be treated containing methane and excess oxygen, which comprises supporting platinum, iridium and rhenium on a zirconium oxide carrier.
Compared with a catalyst in which iridium and platinum are supported on a zirconium oxide carrier, this catalyst significantly improves methane oxidation activity at a low temperature of 400 ° C. or lower, and is also excellent in durability over time.

However, there are still problems with the preparation of the catalyst shown in Patent Document 6 from a practical and economic point of view.
The problem is that when carrying iridium and platinum on a zirconium oxide carrier, it is essential to use a chloride-based raw material in order to obtain high activity.

Patent Document 6 discloses two preparation methods for carrying the three components of iridium, platinum and rhenium on a zirconium oxide carrier.

The first method uses a mixed solution of rhenium pentachloride (ReCl ₅ ) prepared by dissolving rhenium chloride (ReCl ₅ ) in hydrochloric acid, hexachloroiridium acid (H ₂ IrCl ₆ ) and hexachloroplatinic acid (H ₂ PtCl ₆ ). , A method in which three components of iridium, platinum and renium are simultaneously supported on a zirconium oxide carrier.

The second method is a method in which ammonium perrhenate is used to first support rhenium on a zirconium oxide carrier, and then a mixed solution of hexachloroiridium acid and hexachloroplatinic acid is used to support iridium and platinum.

In the first method, it is necessary to use a strong hydrochloric acid acidic solution in order to stably dissolve rhenium chloride, which is industrially problematic.
The second method is superior to the first method because the support of rhenium can avoid the use of chloride, but the support of iridium and platinum uses chloride, which is also an industrial problem. There is.
Specific problems in preparing a catalyst using a chloride-based raw material include the following. First, when preparing a honeycomb catalyst, the metal base material cannot be used due to the problem of corrosion due to chlorine content. Further, since highly corrosive hydrogen chloride is generated in the drying and firing steps at the time of catalyst preparation, special equipment having high corrosion resistance is required, which may cause a problem in terms of economy.

Patent Document 4 also shows the activity results of an iridium-platinum / zirconia catalyst prepared using a nitric acid solution of tris (acetylacetonato) iridium, which is an organic metal complex of iridium, and dinitrodiammine platinum. However, the organometallic complex of iridium is not advantageous in terms of economy because it is poorly soluble and difficult to handle in addition to being expensive.

In order to decompose and remove the NOx component contained in the combustion exhaust gas of gas fuel, one or more kinds of iridium, platinum, and rhodium are used on a porous carrier made of one or more kinds of alumina, zirconium oxide, and titanium oxide. A catalyst for removing NOx is proposed (see Patent Document 7). However, this document only shows NOx removal performance and does not teach at all about the removal rate of hydrocarbons, and it is not possible to oxidatively decompose the most persistent methane among hydrocarbons. I haven't suggested it either.

Further, a method for producing an exhaust gas purification catalyst in which at least one of platinum and rhodium and at least one of iridium and ruthenium are supported on an inorganic carrier such as activated alumina by a specific method using citric acid. Is disclosed (see Patent Document 8). According to this document, iridium and / or ruthenium form a solid solution with 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 is improved, and does not teach at all about the oxidative decomposition of methane, which is particularly persistent among the hydrocarbons contained in the exhaust gas. ..

A method for producing a platinum-containing solution for supporting a catalyst, which provides a high-performance platinum-containing catalyst, in which the ratio is 0.01 to 0.5 mol per liter of the dilute nitric acid aqueous solution in a dilute nitric acid aqueous solution of 2.5 or less. A method is known which comprises heating and aging an amount of dinitrodiammine platinum at 90 ° C. to 100 ° C. (Patent Document 9). However, this document only shows the exhaust gas purification performance under the theoretical air-fuel ratio condition of gasoline engine exhaust gas using platinum or platinum-logium catalyst, and methane is particularly persistent among various hydrocarbons present in the exhaust gas. Therefore, it does not reveal at all how methane in exhaust gas containing excess oxygen can be efficiently oxidatively decomposed.

Japanese Unexamined Patent Publication No. 51-106691 Japanese Unexamined Patent Publication No. 8-332392 Japanese Unexamined Patent Publication No. 11-319559 International Publication No. 2002/040152 JP-A-2009-112912 Japanese Unexamined Patent Publication No. 2012-96221 Japanese Unexamined Patent Publication No. 3-293035 Japanese Unexamined Patent Publication No. 3-98644 Special Publication No. 63-27053

Applied Catalysis B: Environmental, Vol. 14, 1997, p. 211-223 Catalysis Letters, Vol. 141, 2011, p. 413-419

An object of the present invention is high methane resolution even at low temperatures without using chloride-based raw materials, which have various economical problems regarding the oxidation removal of methane in a gas to be treated containing methane, sulfur compounds and excess oxygen. It is an object of the present invention to provide a method for producing a catalyst exhibiting the above, and a method for oxidizing and removing methane in a gas to be treated using the catalyst produced by this method.

The characteristic composition of the method for producing a catalyst for removing methane oxidation of the present invention for achieving the above object is that nitric acid containing perrhenic acid or a salt thereof, iridium nitrate and dinitrodiammine platinum are dissolved, and substantially free of chlorine ions. The point is that the zirconium oxide carrier is impregnated with an acidic aqueous solution to support iridium, platinum and perrhenic acid, and then fired.

Another characteristic configuration of the method for producing a catalyst for removing methane oxidation of the present invention for achieving the above object is that iridium nitrate and dinitrodiammine platinum are dissolved in a zirconium oxide carrier carrying renium in advance , and substantially chlorine ions are formed. It is characterized in that it is impregnated with a nitric acid acidic aqueous solution containing no iridium to support iridium and platinum, and then calcined.

In the above configuration, the nitric acid acidic aqueous solution before impregnating the zirconium oxide carrier may be aged at a temperature of room temperature to 75 ° C. In the present invention, the normal temperature means 5 ° C. or higher and 35 ° C. or lower.

Further, in the above configuration, the nitric acid acidic aqueous solution may further contain a polyvalent carboxylic acid.

Further, in the above configuration, at least one of citric acid, malic acid and tartaric acid may be contained as the polyvalent carboxylic acid.

Further, the characteristic configuration of the methane oxidation removal method of the present invention for achieving the above object is a methane oxidation removal method for oxidizing and removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen. The point is that the gas to be treated is brought into contact with the catalyst produced by the above method at a temperature of 300 ° C. or higher and 450 ° C. or lower.

The catalyst for removing methane oxidation produced by the method of the present invention exhibits extremely excellent resistance to activity inhibition by water vapor and sulfur compounds, and therefore produces a large amount of water vapor like combustion exhaust gas, which is an example of a gas to be treated. It exhibits high methane oxidation activity even in exhaust gas containing sulfur oxides.
Further, in the method for producing a catalyst for removing methane oxidation of the present invention, since chloride is not used as a raw material, highly corrosive hydrogen chloride is not generated, which is excellent in economy.

The method for producing the catalyst for removing methane oxidation and the method for removing methane oxidation according to the embodiment of the present invention will be described below. In addition, although preferable examples are described below, each of these examples is described in order to more specifically exemplify the present invention, and various modifications can be made without departing from the spirit of the present invention. However, the present invention is not limited to the following description.

The method for producing a catalyst for removing methane oxidation for oxidizing and removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen is nitric acid in which perrhenic acid or a salt thereof and iridium nitrate and dinitrodiammine platinum are dissolved. The zirconium oxide carrier is impregnated with an acidic aqueous solution to support iridium, platinum and perrhenic acid, and then fired.

If the surface area of the carrier, zirconium oxide, is too small, the catalytically active component cannot be kept highly dispersed. On the other hand, if the surface area is too large, the thermal stability of zirconium oxide is not sufficient, and the sintering of zirconium oxide itself may proceed during the use of the catalyst.

The specific surface area of zirconium oxide used as a carrier (referred to in this specification as the specific surface area by the BET method) is usually about 2 to 90 m ² / g, preferably about 10 to 30 m ² / g. The crystal form of zirconium oxide is preferably monoclinic, but may contain 25% or less tetragonal or cubic crystals 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 zirconium oxide may be prepared by using commercially available zirconium oxide for a catalyst carrier as it is, or by calcining at 500 ° C. to 800 ° C. in an oxidizing atmosphere such as air.

Zirconium oxide used as a carrier may contain a trace amount of components other than zirconium oxide such as alumina and silica in order to improve adhesion to a support such as cordierite and sinterability, but these components Should not exceed 2% on a mass basis.

If the amount of platinum, iridium, and rhenium supported on zirconium oxide is too small, the catalytic activity will be low, but if it is too large, the particle size will be large, and the supported catalytically active components will be effectively utilized. It disappears.

The amount of platinum supported is preferably about 0.5 to 20%, more preferably about 0.5 to 5% in terms of mass ratio to zirconium oxide. The amount of iridium supported is preferably about 0.5 to 20%, more preferably about 0.5 to 5%, in terms of mass ratio to zirconium oxide. The ratio of the supported amount of platinum to iridium is preferably about 0.3 to 5 in terms of the mass ratio of iridium / platinum, and more preferably about 1 to 2.

The amount of rhenium supported is preferably about 0.1 to 10%, more preferably about 0.2 to 2% in terms of mass ratio to zirconium oxide. The ratio of the amount of platinum and rhenium carried is preferably about 0.1 to 2 in terms of the mass ratio of rhenium / platinum, and more preferably about 0.2 to 1.

In the method for producing a catalyst for removing methane oxidation of the present invention, an acidic nitrate aqueous solution containing a predetermined amount of iridium, platinum and rhenium is prepared by dissolving iridium nitrate or a salt thereof and iridium nitrate and dinitrodiammine platinum. Is impregnated with a zirconium oxide carrier to support iridium, platinum and rhenium.

As the nitric acid acidic aqueous solution in which ammonium perrhenic acid or a salt thereof and iridium nitrate and dinitrodiammine platinum are dissolved, for example, each nitric acid acidic aqueous solution of iridium nitrate and dinitrodiammine platinum is prepared, and the mixture thereof is mixed with perrhenic acid. It can be prepared by dissolving ammonium. Instead of ammonium perrhenate, rhenium oxide (Re ₂ O ₇ ) or perrhenic acid obtained by dissolving this in water may be used, but cations such as potassium perrhenate remaining in the catalyst after firing may be used. The use of containing perrhenic acid compounds may reduce the activity of the catalyst.

A catalyst with higher activity can be obtained by aging an acidic nitrate aqueous solution in which perrhenic acid or a salt thereof and iridium nitrate and dinitrodiammine platinum are dissolved by a predetermined method. Aging is carried out at a temperature of room temperature to 90 ° C. for about 30 minutes to 30 days. The higher the temperature, the shorter the aging time, which may be about 20 days at room temperature and about 1 hour at 75 ° C. If the aging time is too short, there is no effect, and if it is too long, the dispersity of the catalyst decreases and the activity decreases. Although the mechanism of aging is unknown, it is possible that the condensation of iridium and platinum complexes to form clusters promotes the formation of a supported state in which iridium and platinum are uniformly mixed at the atomic level.

Instead of aging, a polyvalent carboxylic acid is added to achieve the same effect. This is presumed to have the same effect as Patent Document 8, but it is considered that the effect is actually different. In Patent Document 8, the state of the active metal is in the metallic state, whereas in the catalyst prepared by the production method of the present application, the active metal is in the oxidized state, so that a solid solution as in Patent Document 8 is not formed. Be done.

The polyvalent carboxylic acid includes a hydroxycarboxylic acid having a hydroxyl group.
Preferred as the polyvalent carboxylic acid is an aliphatic, short-chain polyvalent carboxylic acid. Particularly preferred are hydroxycarboxylic acids. As the hydroxycarboxylic acid, citric acid, malic acid and tartaric acid are preferable.
Long-chain carboxylic acids and aromatic carboxylic acids have a small number of carboxyl groups per molecular weight, which reduces their effect per mass and excessively reduces iridium and platinum during the catalyst firing process. Therefore, the methane oxidation activity may be impaired.

If the amount of the polyvalent carboxylic acid added is too small, the effect is weak, and if it is too large, the effect may be impaired. The amount of the polyvalent carboxylic acid added to the nitric acid acidic aqueous solution is preferably about 0.2 to 5.0, more preferably about 0.2 to 5.0 by mass ratio of (polyvalent carboxylic acid) / (platinum + iridium) in the nitric acid acidic aqueous solution. It is about 0.2 to 2.0, more preferably about 0.5 to 2.0. Alternatively, the amount of substance of the carboxyl group of the polyvalent carboxylic acid is preferably about 0.6 to 20 times, more preferably 0.6 to 10 times the total amount of substance of iridium and platinum ions in the acidic aqueous solution of nitric acid. It may be about twice, more preferably about 0.6 to 6 times.

The impregnation time is not particularly limited as long as a predetermined carrying amount is secured, but is usually about 1 to 50 hours, preferably about 3 to 20 hours. Next, zirconium oxide carrying a predetermined metal component is evaporated to dryness or dried at 80 ° C. to 120 ° C. using a heating device such as a hot plate or an evaporator, if necessary, and then calcined.

The firing may be carried out under the circulation of an oxidizing gas. For example, it may be carried out under the circulation of air. Alternatively, it may be carried out under the flow of an oxidizing gas such as air or a gas in which oxygen and an inert gas such as nitrogen are appropriately mixed.

If the firing temperature is too high, the grain growth of the supported metal proceeds and high activity cannot be obtained. On the contrary, if it is too low, firing is not sufficiently performed, 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 firing 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.

Another characteristic configuration of the method for producing a catalyst for removing methane oxidation of the present invention is to impregnate a zirconium oxide carrier previously supported with renium with an acidic aqueous nitrate solution in which iridium nitrate and dinitrodiammine platinum are dissolved to support iridium and platinum. After that, it is fired.

In this case as well, the amount of iridium, platinum, and rhenium supported is the same as in the case where the above-mentioned three components of iridium, platinum, and rhenium are supported at the same time. Further, the aging of the nitric acid acidic aqueous solution or the addition of the polyvalent carboxylic acid can be carried out in the same manner as in the case where the three components are simultaneously supported in the nitric acid acidic aqueous solution in which iridium nitrate and dinitrodiammine platinum are dissolved.

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

When wash-coating on the fire-resistant honeycomb, the catalyst for removing methane oxidation prepared by the above method may be made into a slurry and wash-coated, or after zirconium oxide is wash-coated on the fire-resistant honeycomb in advance. , The active ingredient may be supported by impregnating perrhenic acid or a salt thereof with an acidic aqueous solution of nitric acid in which iridium nitrate and dinitrodiammine platinum are dissolved according to the above impregnation method. In either case, a binder can be added as needed. As a preferred example, a binder (eg, zirconium oxide sol), an appropriate amount of water and, if necessary, a thickener are added to the zirconium oxide carrier to prepare a slurry, which is coated on a fire-resistant honeycomb and dried. By firing at 650 to 750 ° C., a zirconium oxide layer is formed on a fire-resistant honeycomb, and this is impregnated with an acidic aqueous nitrate solution in which perrhenic acid or a salt thereof and iridium nitrate and dinitrodiammine platinum are dissolved to form platinum. Examples include methods of supporting iridium and rhenium. Since the method for producing a catalyst for removing methane oxidation of the present invention does not use a chloride that corrodes the metal carrier, not only a ceramic carrier such as cordierite but also a metal carrier using a stainless steel foil can be adopted.

The method for removing methane oxidation of the present invention is characterized by using a catalyst for removing methane oxidation produced according to the above method.

The target of the methane oxidation removal method of the present invention is a gas containing methane, a sulfur compound and excess oxygen (gas to be treated), which is released from, for example, combustion exhaust gas, coal mine ventilation gas, or various chemical processes. It is gas. In addition to methane, the gas to be treated may contain lower hydrocarbons such as ethane and propane, and flammable components such as carbon monoxide and oxygen-containing compounds. Since these are more easily decomposed than methane, they can be easily oxidized and removed at the same time as methane.

The concentration of the flammable component in the gas to be treated is not particularly limited, but if it is too high, an extreme temperature rise may occur in the catalyst layer, which may adversely affect the durability of the catalyst. The concentration in terms of methane is preferably 1% by volume or less, and more preferably 5,000 ppm or less on a volume basis.

If the amount of the catalyst for removing methane oxidation is too small, an effective removal rate cannot be obtained. Therefore, it is preferable to use an amount having a space velocity (GHSV) per gas time of 500,000 h ^-1 or less. On the other hand, the lower the space velocity per gas time (GHSV), the larger the amount of catalyst, so the purification rate improves, but if the GHSV is too low, it is economically disadvantageous and the 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 gas to be treated is not particularly limited as long as it contains an excess of oxygen than the oxidation equivalent of the reducing component in the gas to be treated, but is about 2% or more (more preferably about 5% or more) as a volume standard. It is preferable that oxygen is present at an amount of about 5 times or more (more preferably about 10 times or more) the oxidation equivalent of the reducing component composed of hydrocarbons and the like.
If the oxygen concentration in the gas to be treated is extremely low, the reaction rate may decrease, so a required amount of air or exhaust gas with excess oxygen may be mixed in advance.

The temperature of the gas to be treated is usually about 300 ° C. or higher and 600 ° C. or lower, preferably about 300 ° C. or higher and 450 ° C. or lower. At a temperature lower than this, the activity of the catalyst for removing methane oxidation becomes insufficient, and an effective removal rate cannot be obtained. On the other hand, when the temperature of the gas to be treated exceeds 600 ° C., or when the concentration of flammable components in the gas to be treated is high and the temperature of the gas to be treated exceeds 600 ° C. at the catalyst outlet, the durability of the catalyst becomes high. May decrease.

According to the methane oxidation removal method of the present invention, methane oxidation removal in the gas to be treated can be stably performed, so that combustion exhaust gas such as methane fermentation gas and natural gas city gas, and coal mine ventilation gas can be used. By treating a gas containing methane and sulfur compounds (an example of a gas to be treated) such as various process gases by a methane oxidation removal method, methane contained in the gas is oxidized and removed, and the reaction heat is recovered. In addition to being effectively used as energy, it also contributes to the improvement of the global environment.

In the case of coal mine ventilation gas, about 1 to 3% by volume of water vapor is contained, and in the combustion exhaust gas, about 5 to 15% by volume of water vapor is contained. However, according to the methane oxidation removal method of the present invention, water vapor is contained in this way. Effective methane oxidation removal is also achieved for exhaust gas.

In addition, the combustion exhaust gas usually contains sulfur oxides that significantly reduce the catalytic activity, but the catalyst for removing methane oxidation shows particularly high resistance to the reduction in activity due to sulfur oxides, so it is based on volume. Even when sulfur oxides of about 0.1 to 30 ppm are contained, the methane conversion rate is not substantially affected. Waste-derived gases such as landfill gas contain sulfur compounds such as hydrogen sulfide and mercaptan, which become sulfur oxides on the catalyst and significantly reduce the catalytic activity. However, the methane oxidation removal method of the present invention. According to the report, even if a sulfur compound of about 0.1 to 30 ppm is contained on a volume basis, the methane conversion rate is not substantially affected.

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

[Example 1] (Preparation of catalyst A)
Zirconium oxide (“N-PC” manufactured by Nippon Denko 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 17 m ² / g).
Dinitrodiammine Platinum (Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ; containing 60.0% platinum) is dissolved by heating in 50 g of 20% nitric acid, and nitrate-acidic dinitrodiammine containing 10.0% by mass as platinum. An aqueous platinum solution was obtained.

A dilute nitric acid solution (8.65 g) of iridium nitrate (Ir (NO ₃ ) ₄ ) containing 8.3% by mass of iridium and an aqueous solution of nitric acid-acidic dinitrodiammine platinum containing 10.0% by mass of platinum (4. 80 g) was mixed, diluted with pure water (10 mL), and ammonium perlenate (0.173 g) was dissolved therein to prepare an aqueous nitric acid solution. 24 g of the above-mentioned calcined zirconium oxide was immersed in this nitric acid acidic aqueous solution, and the impregnation treatment was carried out for 15 hours with appropriate stirring. Further, it is evaporated to dryness on a hot plate, dried in a constant temperature dryer at 120 ° C., and then calcined in air at 550 ° C. for 6 hours to produce 3% Ir-2% Pt-0.5% Re / zirconium oxide (catalyst). A) was obtained.
The specific surface area of this catalyst A was 17 m ² / g.

[Example 2] (Preparation of catalyst B)
A dilute nitric acid solution (8.65 g) of iridium nitrate containing 8.3% by mass of iridium and an aqueous solution of nitric acid-acidic dinitrodiammine platinum (4.80 g) containing 10.0% by mass of platinum are mixed and pure. It was diluted with water (10 mL), and ammonium perlenate (0.173 g) was dissolved therein to prepare an aqueous nitric acid solution. This nitric acid acidic aqueous solution was aged while maintaining the liquid temperature at 60 ° C. for 60 minutes while stirring. A hot plate was used to maintain the liquid temperature. The same calcined zirconium oxide (24 g) as in Example 1 was immersed in the aged acidic aqueous solution of nitric acid, and impregnated for 15 hours with appropriate stirring. After evaporating to dryness and drying at 120 ° C., the mixture was calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt-0.5% Re / zirconium oxide (catalyst B). The specific surface area of this catalyst B was 17 m ² / g.

[Example 3] (Preparation of catalyst C)
A dilute nitric acid solution (8.65 g) of iridium nitrate (Ir (NO ₃ ) ₄ ) containing 8.3% by mass of iridium and an aqueous solution of nitric acid-acidic dinitrodiammine platinum containing 10.0% by mass of platinum (4. 80 g) was mixed, diluted with pure water (10 mL), ammonium perlenium (0.173 g) and 2 g of citrate were added thereto, and the mixture was stirred and dissolved to obtain an aqueous nitric acid solution. The mass ratio of (citric acid) / (iridium + platinum) in the nitric acid acidic aqueous solution is about 1.7, and the substance amount ratio of (carboxyl group of citric acid) / (iridium + platinum) is about 5. 24 g of the same calcined zirconium oxide as in Example 1 was immersed in this nitric acid acidic aqueous solution, and impregnation treatment was performed for 15 hours with appropriate stirring. After evaporating to dryness and drying at 120 ° C., the mixture was calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt-0.5% Re / zirconium oxide (catalyst C).

[Example 4] (Preparation of catalyst D)
Ammonium perrhenate (1.15 g) was stirred and dissolved in pure water (72 g). 80 g of calcined zirconium oxide, which was the same as in Example 1, was immersed in this aqueous solution and impregnated for 15 hours with appropriate stirring. After evaporating to dryness and drying at 115 ° C., the mixture was calcined in air at 500 ° C. for 6 hours to obtain 1% Re / zirconium oxide. That is, zirconium oxide carrying rhenium was obtained in advance.
A dilute nitric acid solution of iridium nitrate (7.57 g) containing 8.3% by mass of iridium and an aqueous solution of nitric acid-acidic dinitrodiammine platinum (4.20 g) containing 10.0% by mass of platinum are mixed and pure. Dilute with water (8 mL), further add malic acid (1 g) and stir to prepare a nitric acid acidic solution. The mass ratio of (malic acid) / (iridium + platinum) in the nitric acid acidic aqueous solution is about 1.0, and the substance amount ratio of (carboxyl group of malic acid) / (iridium + platinum) is about 3.
21 g of the above 1% Re / zirconium oxide was immersed in this nitric acid acidic aqueous solution, and impregnation treatment was carried out for 15 hours with appropriate stirring. After evaporating to dryness and drying at 120 ° C., the mixture was calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt-1% Re / zirconium oxide (catalyst D).

[Reference Example 1] (Preparation of catalyst E)
10 g of dinitrodiammine platinum (containing 60.5% platinum) was dissolved by heating in 50 g of 20% nitric acid to obtain a nitric acid-acidic dinitrodiammine platinum aqueous solution containing 10.1% by mass as platinum.
A dilute nitric acid solution of iridium nitrate (10.84 g) containing 8.3% by mass of iridium and an aqueous solution of nitric acid-acidic dinitrodiammine platinum (5.94 g) containing 10.1% by mass of platinum are mixed and pure. An aqueous nitric acid solution was prepared by diluting with water (10 mL). 30 g of the same calcined zirconium oxide as in Example 1 was immersed in this nitric acid acidic aqueous solution, and impregnation treatment was carried out for 15 hours with appropriate stirring. It was evaporated to dryness on a hot plate, dried in a constant temperature dryer at 120 ° C., and then calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt / zirconium oxide (catalyst E). The specific surface area of this catalyst E was 17 m ² / g.

[Reference Example 2] (Preparation of catalyst F)
0.82 g of hexahydroxocobalamin acid (H ₂ Pt (OH) ₆ ) was dissolved by heating in 16 g of 40% nitric acid. A dilute nitric acid solution (9.57 g) of iridium nitrate containing 8.3% by mass of iridium was mixed thereto. This mixed solution was impregnated with 26.5 g of the same calcined zirconium oxide as in Example 1. It was evaporated to dryness on a hot plate, dried in a constant temperature dryer at 120 ° C., and then calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt / zirconium oxide (catalyst F). The specific surface area of this catalyst F was 17 m ² / g.

[Comparative Example 1] (Preparation of catalyst G)
The same as in Reference Example 2 except that a nitric acid solution of hexahydroxoplatinic acid and a dilute nitric acid solution of iridium nitrate were mixed, and then ammonium perrhenate (0.38 g) was added to dissolve the mixture before use for impregnation. 3% Ir-2% Pt-1% Re / zirconium oxide (catalyst G) was obtained. The specific surface area of this catalyst G was 17 m ² / g.

[Reference Example 3] (Preparation of catalyst H)
A dilute hydrochloric acid solution (11.2 g) of hexachloroiridium acid (H ₂ IrCl ₆ ) containing 8.6% by mass of iridium and an aqueous solution (3) of hexachloroplatinic acid (H ₂ PtCl ₆ ) containing 16.3% by mass of platinum. .93 g) was mixed and diluted with pure water (14 mL) to obtain an acidic nitrate aqueous solution. This nitric acid acidic aqueous solution was impregnated with 32 g of the same calcined zirconium oxide as in Example 1. It was evaporated to dryness on a hot plate, dried in a constant temperature dryer at 120 ° C., and then calcined in air at 550 ° C. for 6 hours to obtain 3% Ir-2% Pt / zirconium oxide (catalyst H). The specific surface area of this catalyst H was 17 m ² / g.

[Reference Example 4] (Preparation of catalyst I)
3% Ir-2% Pt-1% Re / zirconium oxide (catalyst I) was obtained in the same manner as in Reference Example 3 except that the same 1% Re / zirconium oxide as in Example 4 was used instead of calcined zirconium oxide. .. The specific surface area of this catalyst I was 17 m ² / g.

[Activity evaluation test]
The catalysts A to I prepared in Examples 1 to 4, Reference Examples 1 to 4, and Comparative Example 1 were tableted and then crushed to have a particle size of 1 to 2 mm. 1.45 g (about 1.5 mL) of each molded product was filled in a quartz reaction tube (inner diameter 15 mm). Next, a gas having a composition of 1,000 ppm of methane, 10% of oxygen, 10% of water vapor (all based on volume) and residual nitrogen was circulated to the reaction tube at a flow rate of 2 L / min (volume in the standard state), and the catalyst was used. Methane conversion rates at layer temperatures of 375 ° C, 400 ° C, 425 ° C and 450 ° C were measured (“early” methane conversion). The gas composition before and after the reaction was measured by a gas chromatograph having a hydrogen flame ionization detector and a thermal conductivity detector. After that, while maintaining the catalyst layer temperature at 450 ° C., 3 ppm of sulfur dioxide was added to the reaction gas to continue the reaction, and at the respective time points after 20 and 60 hours, the catalyst layer temperatures were 375 ° C., 400 ° C. and 425 ° C. And the methane conversion rate at 450 ° C. was measured in the same manner (methane conversion rate after "20 hours" and "60 hours"). Under all catalyst and reaction conditions, 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 the methane conversion rate. Here, the methane conversion rate is a value obtained by the following formula.
Methane conversion rate (%) = 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.

The catalyst H of Reference Example 3 prepared by supporting iridium and platinum using chloride on zirconium oxide showed an initial methane conversion rate of 87% at 400 ° C., 82% after 20 hours, and after 60 hours. However, it maintained a high value of 80%.
Further, the catalyst I of Reference Example 4 prepared by supporting iridium and platinum using chloride on zirconium oxide supporting rhenium in advance showed a methane conversion rate of 92% at 400 ° C. at the initial stage, and 20 hours later. It maintained a high value of 86% and 86% even after 60 hours.
When iridium and platinum are supported using chloride in this way, high methane-oxidizing activity can be obtained, and by adding rhenium, low-temperature activity is improved and the stability of activity over time is improved. Was confirmed.

On the other hand, in the catalyst F of Reference Example 2 prepared by supporting iridium and platinum using iridium nitrate and hexahydroxoplatinic acid in order to avoid problems related to the use of chloride, the methane conversion rate at 400 ° C. The initial value was 59%, 20 hours later was 66%, and 60 hours later was 62%, which were low values.
Even with the catalyst G to which rhenium was added, the methane conversion rate at 400 ° C. was 78% at the initial stage, 65% after 20 hours, and 67% after 60 hours.
Compared with the methane conversion rate of the catalyst F, the methane conversion rate of the catalyst G showed an improvement in low temperature activity and an improvement in the stability of the activity over time due to the addition of rhenium, but the level of activity was low. It was.

On the other hand, in the catalyst A prepared by the production method of the present invention, the methane conversion rate at 400 ° C. was 81% at the initial stage, 75% after 20 hours, and 75% after 60 hours. The activity level of catalyst A is high, and compared with the catalyst to which rhenium is not added (Reference Example 1, catalyst E), the activity level is comparable, and methane 20 hours and 60 hours after the start of the reaction. As is clear by comparing the conversion rates, the catalyst A is superior in the stability of the activity over time, and the effect of adding rhenium is exhibited.

Further, the activities of the catalyst B obtained by aging the nitric acid acidic aqueous solution before impregnating the zirconium oxide carrier, the catalyst C obtained by adding citric acid to the nitric acid acidic aqueous solution, and the catalyst D adding malic acid were remarkably improved. In particular, catalyst C showed methane-oxidizing activity that was not much different from that of catalyst I prepared using chloride. Further, like the catalyst D, a methane oxidation catalyst having excellent activity and stability over time even when impregnated with a nitric acid acidic aqueous solution in which iridium nitrate, dinitrodiammine platinum and malic acid are dissolved in zirconium oxide carrying rhenium in advance. I was able to get.

The production method of the present invention can economically obtain a catalyst exhibiting high methane oxidation activity even in an exhaust gas containing a large amount of water vapor and sulfur oxides such as combustion exhaust gas. Therefore, the oxidation removal of methane in the gas to be treated can be economically advantageous.

Claims (6)

A method for producing a catalyst for removing methane oxidation for oxidizing and removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen, in which perlenic acid or a salt thereof is dissolved with iridium nitrate and platinum dinitrodiammine. A method for producing a catalyst for removing methane oxidation, which comprises impregnating a zirconium oxide carrier with a nitric acid acidic aqueous solution substantially free of chlorine ions to support iridium, platinum and renium, and then firing the catalyst. A method for producing a catalyst for removing methane oxidation for oxidizing and removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen. Iridium nitrate and dinitrodiammine platinum are used on a zirconium oxide carrier supporting renium in advance. A method for producing a catalyst for removing methane oxidation , which comprises dissolving the catalyst, impregnating it with an acidic aqueous nitric acid solution containing substantially no chlorine ions to support iridium and platinum, and then calcining the catalyst. The method for producing a catalyst for removing methane oxidation according to claim 1 or 2, wherein the nitric acid acidic aqueous solution before impregnating the zirconium oxide carrier is aged at a temperature of room temperature to 75 ° C. The method for producing a catalyst for removing methane oxidation according to any one of claims 1 to 3, wherein the nitric acid acidic aqueous solution further contains a polyvalent carboxylic acid. The method for producing a catalyst for removing methane oxidation according to claim 4, wherein the polyvalent carboxylic acid contains at least one of citric acid, malic acid, and tartaric acid. A method for oxidatively removing methane in a gas to be treated containing methane, a sulfur compound and excess oxygen, wherein the gas to be treated is at a temperature of 300 ° C. or higher and 450 ° C. or lower, according to any one of claims 1 to 5. A method for removing methane oxidation in contact with a catalyst produced by the method according to item 1.