JP2009189911A - Catalyst body selectively oxidizing carbon monoxide, filter using it and device for selectively removing carbon monoxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst body selectively oxidizing carbon monoxide removing by oxidation carbon monoxide, prior to hydrogen, contained in a reforming gas (hydrogen rich gas) which is used as the fuel of a fuel cell, and to provide a filter and a device for selectively removing carbon monoxide. <P>SOLUTION: The catalyst body selectively oxidizing carbon monoxide possesses a catalyst material catalyzing the oxidation reaction of carbon monoxide prior to the oxidation reaction of hydrogen in the presence of steam in a hydrogen rich gas at least containing carbon monoxide, and a water feeding body carried in contact with the catalyst material and feeding steam to the vicinity of the catalyst material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a carbon monoxide selective oxidation catalyst body that selectively oxidizes and removes carbon monoxide contained in hydrogen gas, and in particular, a carbon monoxide selective oxidation catalyst body suitable for a fuel cell and a filter using the same. Therefore, it relates to carbon monoxide selective removal equipment.

  Unlike primary batteries and secondary batteries, hydrogen-oxygen fuel cells are attracting attention as energy sources that can continuously extract power by continuously supplying a fuel such as hydrogen and an oxidant such as oxygen. This is a device that directly generates "electricity" by chemically reacting hydrogen and oxygen. This hydrogen-oxygen fuel cell using hydrogen as a fuel has the following characteristics.

(1) Unlike a heat engine (such as an engine or thermal power generation), a fuel cell can be converted directly into electrical energy, so it has high theoretical efficiency.
(2) Because it operates at low temperatures, it does not generate harmful substances such as nitrogen oxides (NOx) and sulfides (SOx) unlike heat engines.
(3) “Hydrogen” as fuel can be made from various materials.
(In addition to fossil fuels such as oil, coal, natural gas, and methanol, water is electrolyzed)

  Hydrogen used as a fuel for a hydrogen-oxygen fuel cell hardly exists in hydrogen gas (a state used as a fuel for a fuel cell as it is). Hydrogen can be produced from fossil fuel, water, biomass, etc. by applying energy such as heat and electricity, but because it is simpler than other raw materials and can be produced at low cost, most of hydrogen is currently fossil fuel (mainly Natural gas).

For example, the process of producing (synthesizing) hydrogen from natural gas consists of steam reforming of natural gas, partial oxidation, and subsequent shift reaction. Here, the “shift reaction” is a reaction (CO + H ₂ O → CO ₂ + H ₂ ) that can occur other than the oxidation of carbon monoxide (CO + O ₂ → CO ₂ ) or the oxidation of hydrogen (O ₂ + H ₂ → H ₂ O). ).

  Hydrogen (hydrogen-rich gas) obtained in this step contains 1-2% of carbon monoxide, which is inevitable in equilibrium, and the carbon monoxide is covered by a platinum-based catalyst used as a fuel electrode of a fuel cell. Causes poison.

  Furthermore, in a fuel cell for home use, a reformed gas type fuel cell is generally used that synthesizes hydrogen by reforming a fuel gas such as city gas and uses this hydrogen as a fuel electrode of the fuel cell. . Even in this reformed gas fuel cell, hydrogen is synthesized from city gas in the same manner as described above, so that 1-2% of carbon monoxide, which is inevitable in equilibrium, remains. Therefore, an oxidation removal technique for reducing the concentration of carbon monoxide, which is an impurity in hydrogen, to a level of several tens of ppm or less is demanded, and a carbon monoxide removal method is actively developed.

  Among the carbon monoxide removal methods currently under development, the most promising method is to add oxygen to the reformed gas (hydrogen-rich gas) and use a precious metal catalyst such as Pt, Pd, Ru, Rh, or Au. This is a method of removing carbon dioxide by oxidizing it to carbon dioxide, and various investigation results have been reported.

  However, this method has a problem in that hydrogen is wasted because hydrogen oxidation proceeds simultaneously with the oxidation of carbon monoxide, and the amount of hydrogen is reduced accordingly.

  In order to solve this problem, it is desirable to selectively oxidize carbon monoxide in preference to hydrogen among the oxidation of hydrogen and carbon monoxide. This is because carbon monoxide can be efficiently removed without wasteful consumption of hydrogen such that hydrogen is oxidized.

Here, the following Patent Documents 1 and 2 have been proposed as techniques relating to a carbon monoxide selective oxidation catalyst that oxidizes carbon monoxide in preference to hydrogen.
Japanese Patent Laid-Open No. 11-347414 JP 2002-263501 A

  Patent Document 1 discloses a technique for oxidizing and removing carbon monoxide in the pores of a porous zeolite. Since hydrogen is smaller than oxygen and carbon monoxide and quickly passes through the pores of the zeolite, it takes advantage of the fact that oxygen and carbon monoxide easily react in the pores because of the long residence time in the pores. is doing.

  Similarly, Patent Document 2 is a technique for oxidizing and removing carbon monoxide in pores. By strengthening the bond between Pt and oxygen, carbon monoxide and oxygen are more easily bonded in the pores.

  The above technique oxidizes carbon monoxide in the pores, and the effect is not clear when water is present in hydrogen, especially how many oxygen molecules selectively oxidized carbon monoxide. There is not enough disclosure regarding CO selectivity.

  The inventors of the present invention have made extensive studies to solve the above-mentioned problems. As a result, in the hydrogen-rich gas, the carbon monoxide oxidation removal ability of a catalyst substance such as Pt or Au is enhanced, and the hydrogen is prioritized. In order to promote the selective oxidation reaction that oxidizes carbon oxide, it has been found that moisture should be actively present in the vicinity of the catalyst substance.

  The reason is presumed that if a large amount of water is present in the vicinity of the catalyst substance, (1) a shift reaction is likely to occur, and hydrogen is generated as a result of oxidation removal of carbon monoxide. For example, an active hydroxyl group is formed thereon, and the hydroxyl group reacts with carbon monoxide to generate hydrogen as the carbon monoxide is oxidized and removed.

  Therefore, if there is moisture in the vicinity of the catalyst material, the catalyst is activated, and the activation energy of the reaction in which oxygen is combined with carbon monoxide and oxidized is lowered. This produces a reaction in which oxygen combines with carbon monoxide and oxidizes rather than a reaction in which oxygen combines with hydrogen and oxidizes. Therefore, oxygen in the hydrogen-rich gas preferentially selects an oxidation reaction that combines with carbon monoxide in preference to hydrogen.

  The present invention has been completed on the basis of the above-described knowledge, and it is preferable to selectively oxidize and reduce carbon monoxide in the reformed gas (hydrogen-rich gas) in preference to hydrogen. An object of the present invention is to provide a carbon monoxide selective oxidation catalyst body that obtains hydrogen gas that achieves utilization efficiency and power generation efficiency.

  A first invention for solving the above problem is a catalytic substance that catalyzes an oxidation reaction of carbon monoxide in the presence of water vapor in a hydrogen rich gas containing at least carbon monoxide in preference to an oxidation reaction of hydrogen. And a water supply body that is kept in contact with the catalyst material and supplies water vapor in the vicinity of the catalyst material.

  An example of the carbon monoxide oxidation catalyst of the present invention is shown in FIG. The catalyst body 3 of the present invention has a configuration in which the catalyst substance 2 is held by the moisture supply body 3.

    The water supply body is selected from those having a property of absorbing a trace amount of water contained in a gas such as hydrogen-rich gas containing hydrogen as a main component. Since the moisture supply body is disposed in contact with the catalyst material, a state in which moisture is always present in the vicinity of the catalyst material is created. Moisture present in the vicinity of the catalyst material enhances the carbon monoxide oxidation removal activity of the catalyst material, and promotes a selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen, so that one part of the reformed gas is Carbon oxide can be selectively oxidized to reduce wasteful consumption of hydrogen with high efficiency.

  In the above configuration, the hydrogen rich gas may include oxygen. If it is this structure, the said catalyst substance will also catalyze the oxidation reaction of carbon monoxide and oxygen.

  In general, removal of carbon monoxide by the catalyst body having pores promotes the reaction in the pores. For example, a catalyst body that selectively oxidizes carbon monoxide without oxidizing hydrogen with a short residence time in the pores by utilizing the difference in residence time of hydrogen, carbon monoxide, and oxygen in the pores. Are known. In this method, when the pores are clogged with moisture, hydrogen, oxygen, and carbon monoxide cannot pass through the pores, and thus an oxidation reaction cannot be caused. Therefore, it is necessary not to clog the inside of the pores by using a hydrophobic substance as the substance having pores or by using the catalyst body after removing moisture from the hydrogen gas. However, in the configuration of the present invention, the presence of moisture in the vicinity of the catalyst substance increases the activity of the catalyst substance and removes carbon monoxide, so the pores may be clogged with moisture.

  The water molecules may be water molecules originally present in the hydrogen-rich gas, or moisture may be absorbed into the moisture supply body from the outside. Oxygen, oxygen that is present in the hydrogen-rich gas from the beginning, or hydrogen-rich gas may be injected from the outside.

  In particular, since the hydrogen-rich gas reformed from natural gas or the like contains water vapor, if this water vapor is used, it is not necessary for the water supply body to absorb water from the outside.

  In the above configuration, the catalyst substance may be held by the moisture supply body with a part of the surface exposed to the outside.

  With this configuration, the catalytic substance can be in direct contact with carbon monoxide, and the catalytic substance can obtain moisture from the moisture supply body, so that the catalytic action is efficiently exhibited.

  In the above-described configuration, the catalyst substance is metal fine particles having an average particle size of at least one selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Ag, Ni, and Au of 1 nm to 10 nm. There can be. When the average particle diameter exceeds 10 nm, the surface area (reaction area) of the catalyst substance is reduced, and the reaction efficiency is deteriorated. On the other hand, if it is less than 1 nm, it is not preferable because it is too fine to handle.

  In the above configuration, the moisture supply body includes a hygroscopic substance, and the catalyst substance is in direct contact with the hygroscopic substance. .

  The moisture supply body may be composed only of having a hygroscopic substance, or may be composed of a hygroscopic substance and another substance. In the latter case, it is preferable that the catalyst material is brought into direct contact with the hygroscopic material because the hygroscopic material absorbs moisture in the hydrogen-rich gas and can reliably supply moisture to the catalyst material.

  In the present invention, the constituent material of the hygroscopic substance includes porous silica, porous alumina, hydrophilic zeolite, silica gel, sodium silicate, polyvinyl alcohol, polyamide, sodium polyacrylate, polymethyl methacrylate, cellulose resin and the like. Can be used. Of these, silica is particularly preferable because silica having different average pore diameters and specific surface areas can be easily produced and has high hygroscopicity.

  In the above-described configuration, the hygroscopic substance may be porous silica having an average pore diameter of 2 nm to 50 nm or less.

In the above configuration, the said hygroscopic material has an average pore diameter of 2 nm to 20 nm, a specific surface area of porous silica of 100m ² / g~500m ² / g, it is configured to, wherein Can do.

  Those having an average pore diameter of 2 to 50 nm are generally called mesopores and have the property of releasing moisture adsorbed at high humidity at low humidity. Further, when the pore diameter is within this range, fine catalyst particles (approximately 1 to 10 nm) are likely to be present in the pores.

Also in the above-described structure, the hygroscopic material has an average pore diameter of 0.5 nm to 2 nm, specific surface area of porous silica of 500m ² / g~1000m ² / g, the structure, characterized in that can do.
Those having an average pore diameter of 0.5 to 2 nm are generally called micropores and have extremely high moisture adsorption ability.

  In the above structure, the hygroscopic substance may be a hydrophilic zeolite.

Since hydrophilic zeolite is excellent in hygroscopicity, it is suitable as a hygroscopic substance. The hydrophilicity of zeolite is related to the molar ratio of SiO ₂ / Al ₂ O _{3 in} the zeolite, and as the molar ratio of SiO ₂ / Al ₂ O ₃ (Kayban ratio) increases, the degree of moisture adsorption decreases. It is known to be. Those having this ratio of 1-2 are called low silica zeolite, and those having a ratio of 5 or more are called high silica zeolite. As the aluminum concentration is lowered, the surface properties change from hydrophilic to hydrophobic. Two or more kinds of these zeolites may be contained.
For example, type A zeolite is representative of low silica zeolite, and ferrierite, ZSM-5 is representative of high silica zeolite.

  A second invention for solving the above-mentioned problems relates to a filter using a carbon monoxide selective oxidation catalyst body. The filter is a carbon monoxide selective oxidation filter having a substrate and the carbon monoxide selective oxidation catalyst body according to the first aspect of the present invention, which is applied to the surface of the substrate directly or via an underlayer. .

  Various substrates can be used as the substrate. Examples include honeycomb structures, powders, spheres, granules, foams, fibers, cloths, or ring structures. In the present invention, it is preferable to use a substrate having a honeycomb structure.

  Since the honeycomb substrate has a large total surface area of the wall surface, the area of the hygroscopic coating layer can be increased, so that more catalyst substance can be disposed and the pressure loss when passing through the hydrogen rich gas is small, so that the hydrogen rich gas can be smoothly flown. Can be passed. For this reason, carbon monoxide contained in the hydrogen-rich gas comes into contact with the catalyst material very efficiently. As a result, the oxidation reaction between carbon monoxide and oxygen proceeds with high efficiency, so that carbon monoxide can be more reliably removed.

Here, from the viewpoint of pressure loss, the honeycomb channel diameter of the honeycomb substrate is preferably 30.
It should be 0 μm or more.

  The honeycomb substrate is preferably made of metal. If it is made of metal, it is easy to manufacture and the manufacturing cost can be reduced. However, since the metal honeycomb substrate has less unevenness on the surface and poor adhesion to the moisture supply body made of porous silica, more preferably fine unevenness is provided between the metal honeycomb substrate and the porous silica layer. It is preferable to form an underlying layer. Thereby, the adhesiveness of the hygroscopic coating layer which consists of porous silica improves.

  The underlayer is preferably a layer made of alumina from the viewpoint of ease of production and cost. Furthermore, since alumina is hydrophilic, the alumina also plays a role of providing moisture near the catalyst material.

  In the above configuration, the alumina may have a surface roughness value of 0.5 μm to 3.0 μm. If it is this range, since the adhesiveness of a porous silica layer and a base | substrate will improve more, it is preferable.

  3rd invention which solves the said subject is related with the carbon monoxide selective removal apparatus incorporating the carbon monoxide selective oxidation filter concerning said 2nd invention. The apparatus includes a hydrogen gas supply unit made of a hydrogen rich gas containing carbon monoxide, an oxygen gas supply unit for mixing the hydrogen gas with a gas containing oxygen, and the carbon monoxide oxidation according to the second aspect of the invention. A catalyst reaction unit including a filter; and a temperature control unit configured to control a temperature of the carbon monoxide selective oxidation filter of the catalyst reaction unit.

  This apparatus mixes hydrogen introduced from the hydrogen gas supply unit with hydrogen-rich gas mainly composed of hydrogen and oxygen introduced from the oxygen gas supply unit to form a mixed gas, and the temperature control unit uses the catalyst reaction unit. The temperature of the carbon monoxide selective oxidation filter is controlled, and the mixed gas is passed through the carbon monoxide selective oxidation filter to selectively remove carbon monoxide contained in the hydrogen-rich gas.

  The temperature in the catalytic reaction section when the mixed gas passes is preferably maintained at 25 ° C to 125 ° C. Within this temperature range, the selective removal efficiency of carbon monoxide can be optimized.

  A preferable temperature range in the catalytic reaction part includes 50 ° C. to 120 ° C. which is the operating temperature of the polymer electrolyte fuel cell. Therefore, any carbon monoxide selective removal apparatus having the above-described configuration can be used for a gas reforming section of a solid polymer fuel cell. In particular, carbon monoxide can be removed from the hydrogen gas immediately before supplying hydrogen to the fuel electrode of the fuel cell.

  Further, in the above configuration, the water vapor uses the water vapor contained in the hydrogen-rich gas. However, when no water vapor exists in the hydrogen-rich gas, a water vapor supply unit for supplying water vapor can be further provided.

As explained above, according to the first invention, carbon monoxide in the hydrogen-rich gas (reformed gas) is selected and oxidized with priority over hydrogen to achieve good fuel utilization efficiency and power generation efficiency. Thus, it is possible to provide a carbon monoxide selective oxidation catalyst body that obtains hydrogen gas.
Further, according to the second invention comprising this catalyst body as a constituent element, a filter that preferentially oxidizes and removes carbon monoxide can be provided.
In addition, according to the third invention having this filter as a constituent element, it is possible to provide a selective carbon monoxide removal device for a fuel cell that is excellent in carbon monoxide removal capability.

(Embodiment 1)
Embodiment 1 shows one aspect of the carbon monoxide selective catalyst according to the present invention. With reference to FIGS. 1-3, the structure of the catalyst body in this invention is demonstrated.

  As shown in FIG. 1, the carbon monoxide selective oxidation catalyst body according to the first embodiment includes a catalyst material 2 and a moisture supply layer 3 that adsorbs and holds the catalyst material.

  The catalyst material 2 is selected from fine particles having an average particle diameter of 10 nm or less selected from Pt, Pd, Ir, Rh, Ru, Ag, Ni, Au, and the like.

  Further, the moisture supply layer 3 is made of porous silica and is supported on the moisture supply layer 3 by adsorbing and holding moisture in the hydrogen-rich gas containing a trace amount of moisture and supplying moisture around the catalyst substance. It functions to enhance the carbon monoxide removal activity of the catalyst material and to promote a selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen.

  The mechanism of water supply to the catalyst material 2 of the porous silica 3 differs depending on the difference between the average average pore diameter of the porous silica 3 and the average particle diameter of the catalyst material 2.

When the average pore diameter of the porous silica is smaller than the average particle diameter of the catalyst substance 2, the catalyst substance 2 is supported in the vicinity of the pores of the porous silica as shown in FIG. In particular, porous silica having pores called micropores having an average pore diameter of 2 nm or less has an extremely high moisture adsorption capacity. For this reason, it is possible to draw the moisture in the atmospheric gas near the porous silica surface. As a result, as shown in FIG. 2, moisture (H ₂ O) is always present around the catalyst material 2, and this moisture enhances the carbon monoxide removal activity of the catalyst material and gives priority to hydrogen. A selective oxidation reaction for oxidizing carbon monoxide can be promoted.

When the average pore diameter of the porous silica is larger than the average particle diameter of the catalyst substance 2, the catalyst substance 2 is supported in and near the pores of the porous silica as shown in FIG. . In particular, porous silica having pores called mesopores having an average pore diameter of 2 to 50 nm or less has a property of releasing moisture adsorbed at high humidity when the moisture is low, although the moisture adsorption ability is inferior to that of micropores. As a result, as shown in FIG. 3, moisture (H ₂ O) always exists around the catalyst material 2 supported in the pores, and around the catalyst material 2 supported in the vicinity of the pores. Moisture in the mesopores is released and supplied. This moisture enhances the carbon monoxide removal activity of the catalyst substance 2 and promotes a selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen.

  In other words, regardless of whether microporous silica or mesoporous silica is used, water in the hydrogen-rich gas is actively used, so that catalytic activity does not decrease due to water saturation, and carbon monoxide is oxidized and removed over a long period of time. it can.

  On the other hand, in the case of micropores, the molecular diffusion rate in the micropores is slow, which may be unsuitable for improving the efficiency of the entire carbon monoxide removal process. In the case of mesopores, since the specific surface area is smaller than that of micropores, the carbon monoxide removal reaction field is reduced, and the reaction efficiency may be deteriorated.

  From these, it is preferable to appropriately set the average pore diameter and specific surface area of the porous silica and the average particle diameter of the catalyst substance according to the actual use environment.

Next, a specific method for producing the catalyst body according to the first embodiment will be described.
(Preparation of sodium silicate solution)
First, put the distilled water was de-ionized beaker, to which is dissolved the sodium silicate solution (manufactured by Wako Pure Chemical Industries, Ltd.), creates a sodium silicate aqueous solution having a concentration C _S is 0.8~1.5mol / L To do. The temperature of the aqueous solution at this time is preferably 20 to 30 ° C.

(Addition of strong acidic ion exchange resin)
H ⁺ type strongly acidic ion exchange resin (Amberlite IR120-H-AG manufactured by Rohm and Haas) is added to the aqueous sodium silicate solution until the pH reaches pH ₁ (2.68 to 5.4). . As the H ⁺ type strongly acidic ion exchange resin, it is preferred to use 24 hours or more soaked H ⁺ -type strongly acidic ion exchange resin in distilled water, soaked in distilled water H ⁺ -type strongly acidic ion exchange resin 60 It is more preferable to use a sieve that is separated through a sieve of mesh or less and passed through the sieve.

(Oxidation removal of strongly acidic ion exchange resins)
When the pH is adjusted to 2.68 to 5.4, the addition of the H ⁺ type strongly acidic ion exchange resin is stopped, and the strongly acidic ion exchange resin in the beaker is removed by sieving.

(polymerization)
When the strongly acidic ion exchange resin is removed, polymerization (gelation) proceeds, and the pH gradually increases accordingly.

(Addition of ammonia)
Then, the aqueous sodium silicate solution, until a pH of pH ₂ (7.98 to 8.24), add aqueous NH ₃ solution. When the pH reaches 7.98 to 8.24, the addition of the NH ₃ aqueous solution is stopped to prepare a silica sol solution.

  When the above solution was allowed to stand and a precipitate was formed, the precipitate was filtered and dried to obtain bulk mesoporous silica.

(Supporting catalyst material)
On the silica (water supply body 3) prepared as described above, platinum (Pt) ultrafine particles having an average particle diameter of 3 nm are supported at a rate of 2.0 g / L. In the loading method, a catalyst substance such as Pt was dispersed in water, and the water supply body was immersed in this dispersion. The carrying amount is adjusted by changing the concentration of Pt or the like in a solution containing ultrafine particles such as Pt. As the solvent at this time, water, alcohol or the like can be used.

  After the immersion, drying, firing, and reduction treatment were performed at about 400 ° C. to prepare a carbon monoxide selective oxidation catalyst body.

  The drying / calcination / reduction treatment temperature is usually higher than 250 ° C. and not higher than 700 ° C., and a temperature of 300 to 500 ° C. is preferable because the catalyst activity is remarkably improved. On the other hand, if the temperature is 250 ° C. or lower, calcination / reduction is insufficient, and if it is higher than 700 ° C., aggregated aggregation of the catalyst material particles occurs and the catalyst function is lowered.

(Embodiment 2)
In the second embodiment, the carbon monoxide selective oxidation catalyst is applied to the surface of a substrate to form a carbon monoxide selective oxidation filter. A specific manufacturing method of the filter of the present embodiment is as follows.

  A sodium silicate aqueous solution is prepared in the same manner as in (Preparation of sodium silicate solution), (Addition of strong acid ion exchange resin) and (Oxidation removal of strong acid ion exchange resin) in the first embodiment.

(Preparation of alumina coated metal honeycomb)
In parallel with the above operation, powdered alumina (high purity alumina powder manufactured by Daimei Chemical Industry Co., Ltd.) is diffused in water, alcohol, etc. to prepare an alumina sol. A metal honeycomb 5 (SUS (stainless steel) honeycomb (honeycomb channel diameter: 300 μm or more)) is immersed in the alumina sol, dried and fired to form an alumina layer 4 on the metal honeycomb substrate 5.
Preferably, the value of the surface roughness of the powdered alumina coated on the metal honeycomb is 0.5 to 3.0 μm, and the average pore diameter is 50 nm or more.
The surface roughness value can be determined by observing an image using an atomic force microscope (Nano Scope IIIa manufactured by Digital Instruments) and processing the image using attached image processing software.

(Immersion in silica solution)
The metal honeycomb formed with the powder alumina layer prepared above is immersed in the silica sol preparation solution prepared above for 5 to 10 seconds at 5 to 25 ° C., and then moisture is removed by dry oxidation. This immersion / drying cycle is repeated 10 to 20 times.

(Expansion of silica pores)
By immersing silica in a saturated NH ₃ aqueous solution having a concentration d (10% or more) at a temperature T ₁ (20 ° C. to 60 ° C.) for t _{NH 3} (5 to 50 hours), the pore diameter of silica is expanded. This step is mainly necessary when creating a silica layer having mesopores, and may be omitted when creating silica having micropores.

(Preparation of silica layer)
Then, T _pri (0.1 to 1 hour) is left in an atmosphere of 20 ° C. to 30 ° C. and a humidity of 30 to 60%. After standing, the moisture supply layer 3 made of silica is formed on the alumina layer 4 by aging by leaving T _sec (1 to 2 hours) in a constant temperature bath at T ° C. (100 to 130 ° C.).

(Supporting catalyst material)
On the silica layer (water supply body 3) thus prepared, 0.5 g / L to 2 g of ultrafine particles 4 such as Pt, Au, Rh, Ag, Pd, and Ir having an average particle diameter of 1 to 10 nm are formed. It is supported at a ratio of / L. The supporting method is performed by immersing the honeycomb body after the silica layer coating in a solution containing ultrafine particles such as Pt, and drying, firing, and reducing at about 400 ° C. The carrying amount is adjusted by changing the concentration of Pt or the like in a solution containing ultrafine particles such as Pt. As the solvent at this time, water, alcohol or the like can be used.

  The carbon monoxide selective oxidation filter was produced by applying the carbon monoxide selective oxidation catalyst body to the substrate as described above. As shown in FIG. 2, this is formed on a metal honeycomb substrate 5, an underlayer (alumina layer) 4 having irregularities formed on the wall surface of the metal honeycomb substrate 5, and the alumina layer 4. The catalyst body 1 is provided. The catalyst body 1 is porous silica having an average pore diameter of 50 nm or less as the water supply body 3, and an average particle diameter of Pt, Pd, Ir, Rh, Ru, Ag, Ni, Au, etc. in the water supply body 3 It is formed with the catalyst substance 2 of 10 nm or less.

  The drying / calcination / reduction treatment temperature in the above is usually a temperature exceeding 250 ° C. and 700 ° C. or less. In particular, a temperature of 300 to 500 ° C. is preferable because the catalytic activity is remarkably improved. On the other hand, if the temperature is 250 ° C. or lower, calcination / reduction is insufficient, and if it is higher than 700 ° C., aggregated aggregation of the catalyst material particles occurs and the catalyst function is lowered.

[Relationship between fabrication conditions and physical properties of silica]
Table 1 below shows the relationship between the production conditions of the carbon monoxide selective oxidation filter produced according to the method described in the above embodiment, and the BET specific surface area and average pore diameter of silica, which is a hygroscopic coating layer.
The BET specific surface area S _BET (m ² / g) is measured by measuring the nitrogen adsorption / desorption isotherm using an automatic gas adsorption device (BELSORP MINI, manufactured by Nippon Bell Co., Ltd.), and the BET plot is plotted against the obtained adsorption / desorption isotherm. Applied, analyzed and calculated.
The average pore diameter d _p was obtained by applying the t-plot method to the nitrogen adsorption / desorption curve to obtain the mesopore volume V _mes , and the following formula.

The specific production conditions were as follows: sodium silicate solution manufactured by Wako Pure Chemical Industries, Ltd. was used as the sodium silicate solution, and Amberlite IR120 manufactured by Rohm and Haas Co., Ltd. as the H ⁺ type strongly acidic ion exchange resin. -H-AG was used, high-purity alumina powder manufactured by Daimei Chemical Co., Ltd. was used as the powder alumina, and SUS (stainless steel) honeycomb (honeycomb channel diameter: 300 μm or more) was used as the metal honeycomb. Further, the cycle in which the SUS honeycomb was immersed in a silica sol solution at 25 ° C. for 5 seconds and then dried was repeated 10 times.

In Table 1 above, C _s is the concentration of the aqueous sodium silicate solution, pH ₁ is the pH of the aqueous solution at the end of ion exchange with the strongly acidic ion exchange resin, and pH ₂ is the pH of the aqueous solution after addition of the NH ₃ aqueous solution. t _pri is the aging time from when the SUS honeycomb is immersed in the silica sol until it is put into the thermostat without being immersed in ammonia water, d is the NH ₃ concentration of the aqueous solution immersed in the silica sol after being immersed in the SUS honeycomb, and T ₁ is NH ₃ Temperature when immersed in an aqueous solution, t _NH3 is the time of immersion in an NH ₃ aqueous solution, T ₂ is the temperature of the thermostat, and t _sec is the aging time in the thermostat.

The average pore diameter d _p of the silica of the silica layer in the carbon monoxide selective oxidation filter was 1.00 to 7.60 nm, and the BET specific surface area S _BET was 117 to 794 m ² / g.

Example 1
A filter according to Example 1 was manufactured according to the method described in the second embodiment. The specific water supply body (silica layer) production conditions used were those shown in (a) of Table 1 above. Pt was used as the catalyst, the average particle size of Pt was 3 nm, and the Pt content was 2.0 g / L.
The particle size of the catalyst material of Pt was measured by direct observation with a scanning transmission electron microscope (manufactured by FEI, Tecnai F20).

(Example 2)
A filter according to Example 2 was produced in the same manner as in Example 1 except that the moisture supplier (silica layer) was produced under the conditions of (g) in Table 1 above.

(Comparative Example 1)
A filter according to Comparative Example 1 was produced in the same manner as in Example 1 except that the water supply body (silica layer) was not formed on the alumina layer.

(Experiment 1)
The performance of the catalyst body was evaluated in a glass normal pressure fixed bed flow reactor. A hydrogen-rich reaction gas containing a trace amount of water was circulated, heated to a predetermined temperature, and after becoming steady-state active, the concentration analysis of the outlet gas was performed using online GC (GC Science, GC3200). The composition of the front of the hydrogen-rich reaction gas passed through the _{filter, CO: 1%, O 2} : 1%, CO 2: 20%, H 2 O: 2%, H 2: was balanced. The space velocity (SV value) was 10,000 / hr, the detector was TCD, the column was Porapak Q, Molecular Sieve 13X. The results are shown in Table 2 below.
CO conversion rate = CO decrease concentration / CO introduction concentration = (COin-COout) / COin,
CO selectivity = CO decreasing concentration / O2 decreasing concentration / 2 = (COin−COout) / ((O2in−O2out) / 2).

  The hydrogen-rich gas used this time contains both moisture and oxygen, but when a hydrogen-rich gas without moisture and oxygen is used, it may be introduced from the outside. For example, moisture may be absorbed by silica and oxygen may be injected into the hydrogen rich gas.

  As can be seen from Table 2 above, it can be seen that the Examples are superior to the Comparative Examples in both CO conversion and CO selectivity. In particular, the CO selectivity is almost 100%, and there has been no report on a selective catalyst showing such a high selectivity.

  This is considered as follows. The more water around Pt, the higher the carbon monoxide oxidation removal catalytic activity, and the selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen can be promoted. In the examples, Pt is supported in a hygroscopic silica layer, and the amount of water around Pt is larger than that of the comparative example in which this silica layer is not formed. Therefore, since the Example promotes a higher Pt catalyst activity and a selective oxidation reaction for oxidizing carbon monoxide than the comparative example, the CO oxidation removal rate and the CO selectivity increase.

  Even when Pt, Pd, Ir, Rh, Ru, Ag, Ni, and Au were used in place of Pt, the same results as above were obtained.

  It can also be seen that there is no significant difference in CO oxidation removal rate and CO selectivity between Example 1 using silica having micropores and Example 2 using silica having mesopores. In the mesopores, the pore diameter was confirmed to 20 nm, but no difference was observed in the oxidation removal ability.

  In the above embodiment, the temperature range is 25 ° C. to 125 ° C. This temperature range includes the operating temperature (50 ° C. to 120 ° C.) of the polymer electrolyte fuel cell. It can also be used in a gas reforming section of a molecular fuel cell. In particular, carbon monoxide can be removed from the hydrogen gas immediately before supplying hydrogen to the fuel electrode of the fuel cell, which is beneficial.

(Experiment 2)
Using the filters according to Examples 1 and 2, the hydrogen-rich gas used in Experiment 1 was allowed to flow for 30 days under the same conditions, and then the performance was evaluated in the same manner as in Experiment 1. However, no deterioration was observed.

  This shows that the filters according to Examples 1 and 2 can oxidize and remove carbon monoxide with high efficiency without causing deterioration even when used for a long time.

(Example 3)
Hydrophilic zeolite having an average pore diameter of 0.4 nm (Zeolam A-4 manufactured by Tosoh Corporation) and Pt particles having an average particle diameter of 2 nm as a catalyst substance were mixed at a mass ratio of 10: 1. A carbon monoxide selective oxidation filter coated with the carbon monoxide selective oxidation catalyst body according to Example 3 was produced in the same manner as in the embodiment.
(Comparative Example 2)
Hydrophobic zeolite (high silica zeolite HSZ-900 manufactured by Tosoh Corporation) and Pt particles having an average particle diameter of 2 nm as a catalyst material were mixed at a mass ratio of 10: 1, and Comparative Example 2 was performed in the same manner as in Example 3. The filter which consists of a catalyst body concerning this was produced.
(Experiment 3)
The performance of the catalyst body was evaluated in a glass normal pressure fixed bed flow reactor. The evaluation method was performed under the same experimental conditions as in Experiment 1.

  As can be seen from Table 3 above, Example 3 is superior to Comparative Example 2 in both CO conversion and CO selectivity. In particular, the CO selectivity is 95% or higher at any reaction temperature, and there has been no report on a selective catalyst showing such a high selectivity.

  This is considered as follows. As the moisture around Pt increases, the carbon monoxide oxidation catalytic activity increases, and the selective oxidation reaction that oxidizes carbon monoxide in preference to hydrogen can be promoted. In the examples, Pt is supported in a hygroscopic hydrophilic zeolite, and the amount of water around Pt is larger than that of the hydrophobic zeolite. Therefore, since the Example promotes a higher Pt catalyst activity and a selective oxidation reaction for oxidizing carbon monoxide than the comparative example, the CO oxidation removal rate and the CO selectivity increase.

  Even when Pt, Pd, Ir, Rh, Ru, Ag, Ni, and Au were used in place of Pt, the same results as above were obtained.

  The catalyst body may be filled in a suitable container such as a test holder.

(Embodiment 3)
The third embodiment relates to a carbon monoxide removal apparatus using the second embodiment (carbon monoxide selective oxidation filter described in FIG. 2). Hereinafter, based on FIG. 5, the carbon monoxide removal apparatus concerning Embodiment 3 is demonstrated. FIG. 5 is a schematic diagram of the carbon monoxide removing apparatus according to the third embodiment.

  As shown in FIG. 5, the carbon monoxide removal apparatus includes a hydrogen gas supply unit that takes in hydrogen containing carbon monoxide, an oxygen gas supply unit that takes in oxygen, a water vapor supply unit that takes water vapor into hydrogen gas, And a catalytic reaction section for bringing the catalyst body into contact with a mixed gas of hydrogen gas, oxygen, and water vapor.

  As the carbon monoxide selective oxidation filter, the carbon monoxide selective oxidation filter produced in the second embodiment is used.

  Furthermore, as shown in Tables 2 and 3, the selective removal efficiency of carbon monoxide can be optimized by keeping the temperature in the catalytic reaction section when the mixed gas passes from 25 ° C. to 125 ° C.

  The hydrogen gas from which the carbon monoxide gas has been removed is discharged from the outlet of the catalytic reaction section. When this apparatus was operated, it was confirmed that it functions properly.

  According to the present invention, hydrogen that reduces wasteful consumption of hydrogen by selectively oxidizing and reducing carbon monoxide in the reformed gas (hydrogen-rich gas), and realizes good fuel utilization efficiency and power generation efficiency. It is possible to provide a carbon monoxide selective oxidation catalyst body, a carbon monoxide selective oxidation filter, and a carbon monoxide removal apparatus that obtain gas. Therefore, industrial applicability is great.

1 is a schematic diagram of a catalyst body in Embodiment 1. FIG. 6 is a schematic diagram showing a structure of a honeycomb wall surface of a catalyst body in Embodiment 2. FIG. In Embodiment 2, it is a conceptual diagram which shows the operation | movement of the pore of porous silica when the average pore diameter of porous silica is smaller than the average particle diameter of a catalyst substance. In Embodiment 2, it is a conceptual diagram which shows the operation | movement of the pore of porous silica when the average pore diameter of porous silica is larger than the average particle diameter of a catalyst substance. FIG. 6 is a conceptual diagram of a carbon monoxide selective removal device in a third embodiment.

Explanation of symbols

1 catalyst body 2 catalyst substance (Pt, Pd, Ir, Rh, Ru, Ag, Ni, Au)
3 Moisture supply body (porous silica layer)
4 Alumina layer 5 Metal honeycomb substrate 10 Hydrogen gas supply unit 11 Oxygen gas supply unit 12 Water vapor supply unit 13 Catalytic reaction unit 14 Carbon monoxide selective oxidation filter 15 Temperature control unit 20 Carbon monoxide selective removal device

Claims (15)

A catalytic substance that catalyzes the oxidation reaction of carbon monoxide in preference to the oxidation reaction of hydrogen in the presence of water vapor in a hydrogen-rich gas containing at least carbon monoxide;
A moisture supplier that is held in contact with the catalyst material and supplies water vapor in the vicinity of the catalyst material;
A carbon monoxide selective oxidation catalyst body comprising: In the carbon monoxide selective oxidation catalyst body according to claim 1,
The carbon monoxide selective oxidation catalyst body, wherein the catalyst substance is held by the moisture supply body with a part of the surface exposed to the outside. In the carbon monoxide selective oxidation catalyst body according to claim 1 or 2,
The catalyst material is fine particles of at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Ag, Ni, and Au, and the average particle size thereof is 1 nm or more and 10 nm or less.
A carbon monoxide selective oxidation catalyst characterized by the above. In the carbon monoxide selective oxidation catalyst body according to any one of claims 1 to 3,
The moisture supplier comprises a hygroscopic substance, and the catalytic substance is in direct contact with the hygroscopic substance;
A carbon monoxide selective oxidation catalyst characterized by the above. In the carbon monoxide selective oxidation catalyst body according to claim 4,
It said hygroscopic material has an average pore diameter of 0.5 nm to 2 nm, specific surface area of porous silica of 500m ² / g~1000m ² / g,
A carbon monoxide selective oxidation catalyst characterized by the above. In the carbon monoxide selective oxidation catalyst body according to claim 4,
The hygroscopic substance is porous silica having an average pore diameter of 2 nm to 50 nm or less.
A carbon monoxide selective oxidation catalyst characterized by the above. In the carbon monoxide selective oxidation catalyst body according to claim 4,
It said hygroscopic material has an average pore diameter of 2 nm to 20 nm, a specific surface area of porous silica of 100m ² / g~500m ² / g,
A carbon monoxide selective oxidation catalyst characterized by the above. In the carbon monoxide selective oxidation catalyst body according to claim 4,
The hygroscopic substance is a hydrophilic zeolite,
A carbon monoxide selective oxidation catalyst characterized by the above. A substrate;
The carbon monoxide selective oxidation catalyst body according to any one of claims 1 to 9, wherein the carbon monoxide selective oxidation catalyst body is applied directly or through an underlayer to the surface of the substrate.
Carbon monoxide selective oxidation filter having A honeycomb substrate having a honeycomb structure;
The carbon monoxide selective oxidation catalyst body according to any one of claims 1 to 9, wherein the carbon monoxide selective oxidation catalyst body is applied directly or via an underlayer to the wall surface of the honeycomb substrate.
A carbon monoxide selective oxidation filter having: The carbon monoxide selective oxidation filter according to claim 10,
The honeycomb substrate is a metal honeycomb substrate;
The carbon monoxide selective oxidation filter characterized by the above-mentioned. The carbon monoxide selective oxidation filter according to any one of claims 8 to 11,
The underlayer is alumina;
The carbon monoxide selective oxidation filter characterized by the above-mentioned. The carbon monoxide selective oxidation filter according to claim 12,
The alumina has a surface roughness value of 0.5 μm to 3.0 μm.
The carbon monoxide selective oxidation filter characterized by the above-mentioned. A hydrogen gas supply unit comprising a hydrogen-rich gas containing carbon monoxide,
An oxygen gas supply unit for mixing a gas containing oxygen with the hydrogen gas;
A catalytic reaction section comprising the carbon monoxide oxidation filter according to any one of claims 8 to 13,
A temperature control unit for controlling the temperature of the carbon monoxide selective oxidation filter of the catalytic reaction unit;
Comprising
The carbon monoxide selective removal apparatus characterized by the above-mentioned. In the carbon monoxide selective removal apparatus according to claim 14,
A water vapor supply unit for mixing water vapor with the hydrogen gas;
The carbon monoxide selective removal apparatus characterized by the above-mentioned.