JP4963036B2 - INORGANIC COMPOSITE MATERIAL COMPRISING GOLD ULTRAFINE PARTICLES AND Apatite, PROCESS FOR PRODUCING THE SAME, AND METHOD FOR OXIDATION AND REMOVAL OF MICROCOAL MONOXIDE USING THE SAME - Google Patents

Description

  The present invention relates to a technology for making living space comfortable and harmless, or a high-performance technology for a fuel cell using hydrogen, which is a high-performance technology using gold ultrafine particles. It relates to a catalyst.

Carbon monoxide is a harmful gas, toxicity to the human body is 1000 ppm, headache, headache, nausea, dizziness, etc. appear, and continuous exposure makes it difficult to escape by itself and leads to death (Non-patent Document 1) , The time-weighted average exposure threshold (TLV-TWA) set by the National Council of Occupational Health and Safety is 25 ppm, and the Life and Health Risk Level (30-minute exposure) set by the National Institute of Health and Safety ( IDLH) is 1200 ppm (Non-Patent Document 1).
In living spaces, heating appliances and cooking utensils that use combustion of oil, gas, charcoal, briquettes, etc. have become widespread, and incomplete combustion of the fuel generates a trace amount of carbon monoxide that does not meet the above safety standards. ing. Even in a trace amount, carbon monoxide binds to hemoglobin in the blood and increases the possibility of harming health such as decreased cardiopulmonary function, hypertension, arteriosclerosis, and arrhythmia. In addition, the enforcement of the Health Promotion Act has made it mandatory to set up smoking rooms in public institutions and companies and to separate smoke, but by smoking in a narrow space, the concentration of carbon monoxide is locally increased. Increased, with potential for adverse health effects.
Due to the above circumstances, there is a strong desire to convert carbon monoxide to carbon dioxide by reacting it with oxygen in the air using an air purification filter coated with a carbon monoxide removal catalyst. A high-performance catalyst to satisfy is under development.

  In recent years, fuel cells have attracted attention as a next-generation energy generation system, and hydrogen is often used as a fuel. Hydrogen is produced by reforming hydrocarbon gas or the like, and is produced as a by-product during the reaction. A small amount of carbon oxide remains in the hydrogen. The residual carbon monoxide reacts with the electrode material to inactivate the electrode and significantly shorten the life of the electrode. Therefore, the development of a catalyst that can remove only carbon monoxide while reacting only a small amount of carbon monoxide in hydrogen gas with oxygen to convert it to carbon dioxide while preventing the oxidation of hydrogen to a small amount is eagerly desired. However, a high-performance catalyst that satisfies this requirement is still under development and has not yet been obtained.

  Conventionally, a precious metal catalyst is often used for oxidative removal of carbon monoxide. Precious metals generally refer to eight types of gold, silver, platinum, palladium, rhodium, iridium, ruthenium, and osmium. Among them, the particle size is precisely controlled, and gold (complexed with an appropriate carrier) Au) catalyst is preferably used as an oxidation removal catalyst for carbon monoxide at low temperature and room temperature (Non-patent Documents 2 and 3, Patent Documents 1 to 3). In addition, platinum (Pt) is often used alone or in combination with other metals and is preferably used for oxidative removal of a small amount of carbon monoxide in hydrogen gas (Non-patent Documents 5 and 6, Patent Documents 4 and 5). .

These gold catalysts or platinum catalysts are usually supported on a carrier made of a metal oxide (Patent Document 1, Patent Document 2, Patent Document 4), or supported on a porous body such as activated carbon, silica gel, and alumina. (Patent Document 3 and Patent Document 5) have not yet been used to obtain a high-performance catalyst that can efficiently remove only a small amount of carbon monoxide in air or hydrogen gas as described above. Is the current situation.
High Pressure Gas Safety Technology Second Revised Edition High Pressure Gas Safety Association Masatake Haruta, Catalysis Today 36 (1997) 153-166 Masakazu Date, et al., Catalysis Today 72 (2002) 89-94 Masakazu Date, et al., Angewandte Chemie International Edition Volume 43, Issue 16, Date: April 13, 2004, Pages: 2129-2132 Attila Wootsch, et al. Journal of Catalysis 225 (2004) 259-266 IH Son, et al. Journal of Catalysis 210, 460-465 (2002) Japanese Patent Publication No. 8-295502 Japanese Patent Publication No. 2004-188243 Japanese Patent Publication No. 11-235169 Japanese Patent Publication No. 2003-48702 Japanese Patent Publication No. 2005-246116

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-performance catalyst capable of efficiently removing a small amount of carbon monoxide in air or hydrogen gas. It is in.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have a catalytic function that a novel inorganic composite in which gold ultrafine particles are supported on a specific carrier efficiently remove carbon monoxide. As a result, the present invention has been completed.
The present invention has been completed based on these findings, and is as follows.
(1) Prepared so that the value of the atomic ratio of Ca / P indicating the molar ratio of calcium and phosphorus is less than 5/3, which is a theoretical value derived from the chemical formula Ca ₁₀ (PO ₄ ) ₆ (OH) _{2 of} apatite. A method for producing an inorganic composite material in which apatite composed of calcium and phosphorus is used as a carrier, and gold ultrafine particles are supported on the apatite carrier ,
Gold hydroxide in which the chlorine ligand is replaced with a hydroxide ligand by adding an alkaline solution to an aqueous solution of a gold complex having a chlorine ligand and adjusting the pH to 7.0 or higher The apatite support is obtained by obtaining an electric affinity of the obtained gold hydroxide complex and the surface of the apatite support, or by ion exchange between the obtained gold hydroxide complex and the constituent elements of the apatite. A method for producing an inorganic composite material, comprising a step of supporting a gold hydroxide complex on the surface of a metal.
(2) The method for producing an inorganic composite material according to (1) above, wherein the apatite support is not heated to a temperature exceeding 50 ° C. before the gold ultrafine particles are supported.
(3) An inorganic composite material produced by the production method of (1) or (2 ) above, wherein the gold ultrafine particles have an average particle size of 10 nanometers or less. .
(4) The inorganic composite material according to (3) above , wherein a specific surface area of the composite material supporting the gold ultrafine particles exceeds 50 m ² / g.
(5) A catalyst used for removing carbon monoxide by reacting carbon monoxide with oxygen to convert it to carbon dioxide, which comprises the inorganic composite material of (3) or (4) above. And a catalyst.
(6) A method of oxidizing and removing a trace amount of carbon monoxide in a gas by reacting with oxygen and converting it to carbon dioxide in the presence of a catalyst, thereby detoxifying the gas, wherein the catalyst is the above (3) or (4) A method for oxidizing and removing traces of carbon monoxide, characterized by using the inorganic composite material.
(7) The method for oxidizing and removing trace carbon monoxide according to the above (6), wherein the gas is air or hydrogen.

The inorganic composite material of the present invention provides a high-performance catalytic action that can efficiently remove a minute amount of carbon monoxide in a gas, and in particular, (1) oxidizes a minute amount of carbon monoxide in air. (2) Only a small amount of carbon monoxide in hydrogen gas reacts with oxygen to convert it to carbon dioxide, thereby preventing hydrogen oxidation in a small amount. It provides a catalytic action capable of removing only carbon oxide. In addition, according to the method for producing an inorganic composite material of the present invention, an inorganic composite material having a high specific surface area in which the specific surface area of the composite material after supporting gold exceeds 50 m ² / g, that is, ultrafine particles of gold are efficiently supported. Thus, an inorganic composite material having high contact efficiency with the reaction gas can be obtained. Furthermore, the method for producing an inorganic composite material according to the present invention provides an excellent method for supporting gold ultrafine particles on an apatite support having a Ca / P value of 5/3, which is an atomic ratio of phosphorus and calcium. To do.

  Hereinafter, the inorganic composite material obtained by combining the support made of apatite having a specific calcium / phosphorus atomic ratio and ultrafine gold particles according to the present invention will be described in detail.

The apatite used as the carrier in the present invention can be prepared using a method known in the literature, but a typical preparation method includes calcium nitrate and ammonium dihydrogen phosphate as a precursor. Wet synthesis method used (Sugiyama, S .; Minami, T .; Hayashi, H .; Tanaka, M .; higemoto, N .; Moffat, JBJ Chem Soc., Faraday Trans. 1996, 92, 293) ) And a method of mixing an aqueous calcium chloride solution and an aqueous potassium hydrogen phosphate solution (http://www.ab11.yamanashi.ac.jp/oneday/2.pdf) are well known. The method for preparing the apartite of the present invention is not limited to these methods, and any known method can be applied.
Hereinafter, the apartite composed of calcium and phosphorus represented by the chemical formula Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ will be described in detail.

A wet synthesis method using calcium nitrate and ammonium dihydrogen phosphate as a precursor, which is one of the preferred preparation methods, adjusts the pH in the same way as an aqueous calcium nitrate solution adjusted to an appropriate value with ammonia water or the like. The obtained ammonium dihydrogen phosphate aqueous solution is mixed to obtain a precipitate, which is washed and dried to obtain a carrier. There is also a preparation method of heating and baking at a high temperature of 300 ° C. or higher after drying treatment such as vacuum drying or standing at room temperature, but in the present invention, performing unnecessary heating before supporting gold ultrafine particles, The surface area is likely to decrease due to the progress of crystallization, and it is particularly preferable to avoid heating at 50 ° C. or higher. Due to the preparation at a low temperature, the composite material after supporting the gold has a large specific surface area preferable as a catalyst, for example, 50 m ² / g or more, more preferably (described in accordance with claim 3) 80 m ² / g or more. A product having a specific surface area of 5% is obtained. This means that the obtained inorganic composite material efficiently supports ultrafine gold particles and has high contact efficiency with the reaction gas.

Apatite composed of phosphorus and calcium is represented by the chemical formula Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , and the theoretical atomic ratio of phosphorus and calcium is Ca / P = 5/3. Since this apatite can change the ratio of Ca / P relatively freely, in the present invention, when used as a carrier for supporting gold, the atomic ratio of Ca / P is set to be less than 5/3. Use the prepared one. That is, in the present invention, the apatite used as a carrier for supporting gold ultrafine particles needs to have an Ca / P atomic ratio of less than 5/3 because the potential of the surface of the apatite is It is presumed that this is because the gold hydroxide complex is preferably adsorbed. In the present invention, a particularly preferred atomic ratio is 1.0 to 1.6.

  In the present invention, the average particle size of the ultrafine gold particles supported on the apatite support is such that the gold supported on supports such as titanium oxide, silicon oxide, alumina, and magnesium hydroxide that have been known so far. In view of the fact that the catalyst exhibits high carbon monoxide oxidizing activity in a state of 10 nanometers or less, preferably 5 nanometers or less, it is desirable that the catalyst be 10 nanometers or less, preferably 5 nanometers or less.

Next, a gold compounding method effective for removing carbon monoxide will be described in detail.
As the method for supporting the ultrafine gold particles, the precipitation method that can uniformly support particles having a diameter of 10 nm or less on the surface of the carrier is most preferable.
The outline of the precipitation method is described below. This precipitation method is already known as a technique for supporting gold on a titanium oxide support, but has been successfully applied to an apatite support in which the value of Ca / P, which is the atomic ratio of phosphorus and calcium, is less than 5/3. The examples that have been made are not yet known.

A water-soluble chloroauric acid (tetrachloroauric acid) is dissolved in ion-exchanged water to prepare an acidic aqueous solution. The solution is neutralized by adding alkali, and the pH value is adjusted to 7.0 or more, which is neutral to alkaline. In this case, on the acidic side where the pH value is less than 7.0, the apatite may be dissolved, which is not preferable. The alkali that can be used here is not particularly limited, but sodium hydroxide is most preferable, and other than that, ammonia water, potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, Sodium bicarbonate and the like are also preferably used. At this time, the chlorine ligand (Cl) coordinated to the gold atom is exchanged for the hydroxide ligand (OH). When the hydroxide ions are coordinated to gold, electrical affinity with the surface of the apatite works, and the gold complex is adsorbed on the apatite surface in a highly dispersed state. The slurry after the pH adjustment is maintained at 30 to 80 ° C., and preferably stirred for 1 minute to 24 hours, more preferably 1 hour to 5 hours to stabilize the adsorption state. After the gold complex has been sufficiently adsorbed, it is thoroughly washed with distilled water, ion exchange water, etc., and residual chlorine and gold complex that cannot be adsorbed are washed away and dried by vacuum drying or other methods. Do. Thereafter, after loading the metal, heating at an appropriate temperature is preferable to bring the metal into an active state. The heating temperature for activation is preferably 200 ° C to 700 ° C, and particularly preferably 250 ° C to 450 ° C.
When this method is used, unlike other known methods such as the impregnation method, the gold particles supported on the apatite surface do not aggregate into large particles exceeding 10 nanometers and 10 nanometers or less. It can be supported in the form of almost uniform ultrafine particles.

  The reaction for removing carbon monoxide by reacting it with oxygen from a gas containing a small amount of carbon monoxide has two major uses. One is removal from the air, and the other is removal from hydrogen. Here, the description will focus on the removal in the air, but the present catalyst can also be applied to the removal from hydrogen.

Air can be preferably used in a range from a sufficiently dried state using a desiccant or the like to a relative humidity of 100% corresponding to the highest relative humidity in the daily living space. The catalyst can be used by passing air containing a minute amount of carbon monoxide for some reason, such as incomplete combustion of fuel or smoking sidestream smoke, through a layer filled with catalyst using a pump or fan, etc. The carbon monoxide is converted into carbon dioxide and made almost harmless by contacting it efficiently, for example, by spraying on a support coated with a catalyst. Carbon dioxide also has toxicity such as dyspnea at 2% or more, but at a low concentration of 1% or less, there is very little influence on the human body compared to carbon monoxide.
EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

<Preparation of apatite>
A predetermined amount of calcium nitrate tetrahydrate was weighed with a Teflon (registered trademark) pharmaceutical spoon and dissolved in water in a beaker. Then, it mixed with ammonia water and it was confirmed that it became pH11-12, and it was set as the solution (A). A predetermined amount of diammonium hydrogen phosphate was measured and dissolved in water in a beaker. Thereafter, ion-exchanged water was added until the precipitate formed by mixing with ammonia water in a draft was completely dissolved. It was confirmed that the pH was 11-12. This solution was designated as solution (B).
While the solution (A) was stirred with a stirring blade, the solution (B) was slowly dropped slowly with a dropper or the like to obtain a milky white precipitate. After stirring for 120 minutes with a stirring blade, the mixture was allowed to stand overnight at room temperature to age the precipitate.
The precipitate after aging was washed with ion-exchanged water using a centrifugal separator and finally subjected to suction filtration to separate the precipitate. Thereafter, vacuum drying was performed at room temperature for 48 hours. In the process up to here, the temperature was prevented from exceeding 50 ° C.

Instead of the above predetermined amount, the molar ratio of calcium to phosphorus (Ca / O) is 1.40, 5/3 (≈1.67 or less, described as “1.67”). Three types of apatite were synthesized by the same method so as to be 8. Each specific surface area was measured by the BET method. Apatite with a Ca / P ratio of 1.4 was 199 m ² / g, apatite with a Ca / P ratio of 1.67 was 173 m ² / g, and the Ca / P ratio was 1. The apatite of 8 was 197 m ² / g.

  X-ray diffraction measurement was performed using RIGAKU-RINT2000. As a result of comparison with the monoclinic structure apatite manufactured by Wako Pure Chemical Industries, Ltd., the crystallinity drops due to the sharpness of the peak, etc., but the peak appears at the same position, and there are no unknown peaks that cannot be assigned. Therefore, it was confirmed that an apatite structure was obtained.

<Supporting ultrafine gold particles>
A predetermined amount of chloroauric acid tetrahydrate was weighed and dissolved in ion-exchanged water. After sufficiently dissolving, the pH was adjusted to the range of 8.6 to 8.8 using a diluted solution of sodium hydroxide. Thereafter, the apatite powder after drying was dispersed in the solution, and the slurry was stirred at 70 ° C. for 3 hours. Thereafter, the apatite on which gold was adsorbed was centrifuged, sufficiently washed with ion-exchanged water, and then vacuum-dried overnight at room temperature. Thereafter, the dried apatite powder was heated and fired at 400 ° C. in the air to obtain a purple gold-supported apatite catalyst. Using a sieve, the particle size was adjusted and subjected to the reaction. When the surface area was measured by the BET method, the catalyst prepared using a carrier having a Ca / P ratio of 1.4 was 120 m ² / g, and similarly, the apatite carrier having a Ca / P ratio of 1.67 was 109 m ² / g. The carrier having a / P ratio of 1.8 was 108 m ² / g.

<Measurement of oxidation removal activity of carbon monoxide in air>
100 mg of the catalyst was weighed and filled into a glass reaction tube. Dry air was circulated at 250 ° C. for 30 minutes, heat treatment was performed, and then cooled to a predetermined temperature. Thereafter, the activity of the catalyst was measured by switching to the reaction gas. The reaction gas was dry air containing 1.0% by volume of carbon monoxide, and the flow rate was adjusted with a mass flow controller so that the flow rate was 33 ml / min. Further, the amount of water contained in the reaction gas was measured with a capacitance type dew point meter. The sensitivity of the gas chromatograph (Shimadzu GC-8A) is calibrated with a bypass line that does not pass through the catalyst layer, and the carbon monoxide removal rate, which is the carbon monoxide removal activity of the catalyst, is reduced in the peak area attributed to carbon monoxide. It calculated with the following formula | equation using the quantity.
Removal rate (%) = (Area value of bypass line−Area value after passing through catalyst layer) ÷ (Area value of bypass line) × 100

<Catalyst activity comparison>
In the catalyst preparation method, a catalyst having a Ca / P ratio = 1.4 and a preparation amount of 5.0 wt% of gold dissolved in a solution was prepared at a room temperature (20 ° C.) at one temperature in the gas after passing through the catalyst layer. The carbon oxide content decreased to below the sensitivity limit of the gas chromatograph, and the CO removal rate was 100%, indicating excellent oxidation removal activity. At that time, it was revealed that the temperature of the catalyst layer was slightly increased, and the oxidation reaction of carbon monoxide, which was an exothermic reaction, proceeded. The dew point temperature measured by a dew point meter was −50 ° C.
Further, even when the temperature was lowered to −15 ° C., the conversion rate of carbon monoxide = 100% was maintained. Further, even when the reaction temperature was lowered to -37 ° C, the conversion rate did not fall below 50%. FIG. 1 is a graph showing the results of the CO removal reaction according to this example.

  This activity is disclosed in a recent literature, gold supported on cerium oxide catalyst (Journal of Catalysis 237 (2006) 303-313, Applied Catalysis A: General 299 (2006) 266-273), oxidizing gold. Compared to or better than catalysts supported on iron (Applied Catalysis A: General 291 (2005) 151-161), catalysts supported on zeolite (Applied Catalysis A: General 291 (2005) 162-169) It can be said that it is excellent activity.

<Comparative example>
Using an apatite support prepared by the same method as in the example so that the atomic ratio of Ca / P was 1.67 which is the theoretical value, gold was supported in the same manner as in the example and a CO oxidation reaction was performed. The removal rate was 48.6% at a reaction temperature of −4 ° C., which was inferior to the examples. Moreover, the catalyst prepared so that the atomic ratio of Ca / P was 1.8, which exceeds the theoretical value, was inferior to the examples with a CO removal rate of 64% at a reaction temperature of 2 ° C. From this result, it is clear that the activity is greatly influenced by the charged Ca / P atomic ratio of the carrier, and it is difficult to obtain a sufficient activity with a carrier having a theoretical ratio of 1.67 and a value exceeding that, as in the examples. In addition, it can be clearly seen that the effect of making the Ca / P ratio at the time of preparation smaller than 1.67 is great.

<Measurement of oxidation removal activity of hydrogen in air>
Instead of air gas containing 1.0% carbon monoxide in the above-described activity measurement, air gas containing 1.0% hydrogen was circulated to measure the oxidation removal activity of hydrogen. The measurement apparatus, measurement method, and activity calculation method were performed under the same conditions as in the case of carbon monoxide. The result is shown in FIG. A higher temperature than CO oxidation is required, and a function of oxidizing CO without oxidizing hydrogen necessary for removing CO in hydrogen can be expected, suggesting that it can be an effective catalyst.

<Photograph of ultrafine gold particles supported on apatite by transmission electron microscope>
Catalysts having high carbon monoxide removal performance in the examples were observed using a transmission electron microscope. The result is shown in FIG. In the figure, four arrows indicate representative particles, but these dark gray particles are attributed to gold ultrafine particles and have a diameter of about 2 to 4 nanometers. It was also confirmed that the gold ultrafine particles did not harden in one place and were uniformly dispersed over the entire surface of the carrier.

<Analysis by X-ray diffraction>
X-ray diffraction (XRD) measurement of a highly active catalyst having a Ca / P ratio of 1.4 was performed using a RIGAKU RINT2000 X-ray diffractometer. The results are shown in FIG. In the figure, (1) is a monoclinic structure hydroxyapatite (manufactured by Wako Pure Chemical Industries, Ltd.) measured as a standard sample for comparison. Ca / P is a theoretical value of 1.67. (2) is a carrier with a Ca / P ratio of 1.4 prepared by the wet synthesis method shown in the Examples, and is an XRD pattern immediately after vacuum drying at room temperature (before supporting gold particles). (3) FIG. 4 is an XRD pattern of the catalyst after heat treatment at 400 ° C. for 3 hours after the treatment of supporting the gold particles on the carrier of (2). In (2), the fine peak is not clear compared to the reference sample in (1) or the peak width is wide, but the peak position is almost the same, and the apatite structure has low crystallinity. It can be said that. Further, there is no unknown peak that cannot be attributed to the peak of (1), and the presence of a crystal structure other than the apatite structure cannot be confirmed. (3) is a catalyst after supporting gold particles, but no peak attributed to gold or a gold compound can be confirmed. In XRD, since it is said that a highly dispersed state and particles having a diameter of 4 to 5 nm or less cannot be observed, it was estimated that gold is in the form of ultrafine particles of 4 to 5 nm or less. Further, even when compared with (1) and (2), no significant change in the crystal structure was observed. Therefore, (3) shows that the carrier has an apatite structure with low crystallinity, and in combination with a transmission electron micrograph, preparation of an inorganic material in which gold ultrafine particles are complexed with apatite was successful. It is shown that.

  In the living space, the carbon monoxide removing catalyst of the present invention can be applied to an air purification filter or the like to convert carbon monoxide in the air into carbon dioxide and remove it. Further, in the fuel cell using hydrogen, by using the carbon monoxide removing catalyst of the present invention, only carbon monoxide can be removed while preventing oxidation of hydrogen to a small amount.

The graph which shows the result of CO removal reaction by an Example Graph showing the result of oxidation removal reaction of hydrogen Transmission electron micrograph of the catalyst Comparison of X-ray diffraction patterns of catalyst and reference standard sample

Claims (7)

Calcium prepared so that the value of the atomic ratio of Ca / P indicating the molar ratio of calcium to phosphorus is less than 5/3 which is a theoretical value derived from the chemical formula Ca ₁₀ (PO ₄ ) ₆ (OH) _{2 of} apatite A method for producing an inorganic composite material in which apatite composed of phosphorus is used as a carrier, and gold ultrafine particles are supported on the apatite carrier,
Gold hydroxide in which the chlorine ligand is replaced with a hydroxide ligand by adding an alkaline solution to an aqueous solution of a gold complex having a chlorine ligand and adjusting the pH to 7.0 or higher The apatite support is obtained by obtaining an electric affinity of the obtained gold hydroxide complex and the surface of the apatite support, or by ion exchange between the obtained gold hydroxide complex and the constituent elements of the apatite. A method for producing an inorganic composite material, comprising a step of supporting a gold hydroxide complex on the surface of a metal. 2. The method for producing an inorganic composite material according to claim 1, wherein the apatite carrier is not heated to a temperature exceeding 50 ° C. before the gold ultrafine particles are supported. An inorganic composite material produced by the production method according to claim 1 or 2, the average particle diameter of the ultrafine particles of the gold-free inorganic composite material you wherein a is 10 nm or less. The inorganic composite material according to claim 3 , wherein a specific surface area of the composite material supporting the gold ultrafine particles exceeds 50 m ² / g. 5. A catalyst used for removing carbon monoxide by reacting carbon monoxide with oxygen to convert it to carbon dioxide, which comprises the inorganic composite material according to claim 3 or 4. A method for detoxifying a gas by reacting oxygen with a small amount of carbon monoxide in a gas in the presence of a catalyst to convert it into carbon dioxide, thereby detoxifying the gas, wherein the catalyst according to claim 3 or 4 is used. A method for oxidizing and removing trace amounts of carbon monoxide, characterized by using an inorganic composite material.   The method for oxidizing and removing a trace amount of carbon monoxide according to claim 6, wherein the gas is air or hydrogen.