JP2008279439A - Catalyst for removing carbon monoxide and/or nitrogen oxide and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly durable catalyst which is high in removal activity of CO and/or NO<SB>x</SB>and low in deactivation of the catalyst, and its production method. <P>SOLUTION: The production method of the catalyst carrying gold nanoparticles on iron oxide includes (1) a step for mixing a trivalent iron salt and an inorganic alkaline component in water to obtain an aqueous mixture, (2) a step for adding a gold compound to the obtained aqueous mixture to make a precipitate deposit, and (3) a step for calcining the obtained precipitate, and the catalyst carrying the gold nanoparticles on the iron oxide and produced according to the production method is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon monoxide and / or nitrogen oxide removing catalyst in which gold nanoparticles are supported on iron oxide, and a method for producing the same.

  As an exhaust gas purification catalyst for purifying exhaust gas from an automobile engine, a catalyst in which a noble metal such as Pt, Rh or Pd is supported on a porous oxide carrier such as alumina is widely known.

  In recent years, research on catalysts using Au instead of noble metals such as Pt, Rh, and Pd is also underway. As an example, a catalyst in which Au fine particles are supported on a carrier such as alumina is a combustible gas (CO, etc.). It is known that it has excellent oxidation activity. However, Au fine particles have a problem that heat resistance is low, and in order to overcome this problem, various catalysts having an activity at a low temperature have been proposed.

For example, Patent Document 1 discloses an Au—Fe ₂ O ₃ catalyst obtained by baking a precipitate obtained by adding an aqueous solution of ferric nitrate and chloroauric acid (HAuCl ₄ ) to an aqueous sodium carbonate solution. However, it is described that carbon monoxide can be completely burned even at -30 ° C or lower.

  Patent Document 2 describes that a catalyst obtained by adding an aqueous solution of chloroauric acid and an aqueous solution of sodium carbonate to an aqueous suspension of iron oxide is used for an oxidation catalyst, a reduction catalyst, a combustible gas sensor element, or the like. ing.

In Patent Document 3, a porous ceramic carrier material containing Fe ₂ O ₃ is impregnated with a solution of a gold compound (eg, tetrachloroauric acid-tetrahydrate) or a suspension of a gold compound is used. It is described that the catalyst obtained by calcination after coating can be CO oxidized at temperatures below 50 ° C.

  However, these catalysts have a relatively high activity, but there is much room for improvement because of the remarkable deterioration of the activity when left at room temperature in air.

  In order to solve this problem, Patent Document 4 reports that a composite in which an alkali porous body is allowed to coexist with a catalyst made of iron oxide supporting gold nanoparticles can maintain catalytic activity for a long period of time.

  In recent years, in fuel cells that have been in the limelight, a catalyst capable of highly selectively removing CO from a reformed gas containing hydrogen and CO has been demanded.

  NOx discharged from a thermal power plant or the like is removed by a catalyst using ammonia as a reducing agent at a high temperature (300 ° C. or higher). Also, NOx removal from gasoline engines is performed at high temperatures (500 ° C. or higher), ternary catalysts, that is, hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in exhaust gas. Removal is performed at the same time by oxidizing and reducing the three substances.

On the other hand, an effective catalyst capable of removing NOx discharged from a diesel engine or the like at a low temperature (200 ° C. or less) has not yet been put to practical use.
Japanese Patent Laid-Open No. 60-238148 (for example, Example 2, FIG. 3) JP-A-63-252908 (for example, claim 1) JP-A-2-303539 (for example, claim 1) Japanese Patent Laying-Open No. 2004-188243 (for example, claim 1)

  An object of the present invention is to provide a highly durable catalyst having high carbon monoxide (CO) and / or nitrogen oxide (NOx) removal activity and little deterioration in catalytic activity, and a method for producing the same. There is to do.

In the present invention, as a result of intensive studies in view of the above-described problems of the prior art, a catalyst in which gold nanoparticles are supported on iron oxide (hereinafter also referred to as “Au—Fe ₂ O ₃ -based catalyst”). Focusing on the method of forming iron oxide and the method of precipitating gold nanoparticles on the iron oxide in the manufacturing process, high CO selective oxidation, NO reduction, etc. are possible, and the catalytic activity is less deteriorated. It has been found that a catalyst (excellent in durability) can be obtained. As a result of further research based on this knowledge, the present invention has been completed.

That is, the present invention provides the following _Au-Fe 2 _{O 3} catalyst and a manufacturing method thereof.

  Item 1. A method for producing a catalyst in which gold nanoparticles are supported on iron oxide, (1) a step of mixing a trivalent iron salt and an inorganic alkali component in water to obtain an aqueous mixture, (2) the obtained aqueous solution The manufacturing method including the process of adding a gold compound to a mixture, and depositing a deposit, and the process of (3) baking the obtained deposit.

  Item 2. Item 2. The production method according to Item 1, wherein in step (1), an inorganic alkali component is added to an aqueous solution containing a trivalent iron salt, and the pH is adjusted to 5 to 11 and mixed.

  Item 3. Item 3. The method according to Item 1 or 2, wherein in the step (3), the baking temperature is 100 to 600 ° C.

Item 4. The trivalent iron salt is iron nitrate, iron sulfate or iron chloride, and the inorganic alkali component is MgO, CaO, LiOH, NaOH, KOH, MgO, CaO, Na ₂ CO ₃ , K ₂ CO ₃ , NaHCO ₃ or Item 4. The production method according to any one of Items 1 to _3, which is KHCO ₃ and the gold compound is chloroauric acid, gold chloride, tetrachlorogold (III) ammonium, gold bromide, gold cyanide or gold hydroxide.

  Item 5. Item 5. A catalyst produced by the production method according to any one of Items 1 to 4, wherein gold nanoparticles are supported on iron oxide.

  Item 6. A method for removing CO from a gas containing CO using the catalyst according to Item 5.

  Item 7. A method for removing nitrogen oxides from a gas containing nitrogen oxides using the catalyst according to item 5.

  Item 8. A reformed gas treatment catalyst comprising the catalyst according to Item 2.

  Item 9. A method for removing CO from a reformed gas using the catalyst according to Item 5.

  Item 10. A combustion gas treatment catalyst comprising the catalyst according to Item 5.

  Item 11. A method for removing CO and NO from combustion gas using the catalyst according to Item 5.

  Item 12. A filter comprising the base material carrying the catalyst according to Item 5.

The Au—Fe ₂ O ₃ catalyst of the present invention has a higher CO oxidation activity than a conventional Au—Fe ₂ O ₃ catalyst, and particularly has a high activity even at a relatively low temperature around room temperature.

  In addition, there is a feature that the catalytic activity is hardly deteriorated. In particular, when the catalyst is used continuously for a long time, when it is left in the air for a long time without using the catalyst, or when both are repeated, the deterioration of the catalyst activity is small (that is, high durability) The point) should be noted.

  Moreover, since CO can be oxidized and removed from the mixed gas containing hydrogen and CO with high selectivity, it is effectively used as a catalyst for removing CO from reformed gas for fuel cells, for example.

Further, by treating NO, _CO, combustion gas containing O 2, _{N 2} or the like by using the _Au-Fe 2 _{O 3} catalyst of the present invention to reduce NO almost completely in _{N 2 (N 2} O CO can be oxidized almost completely to CO ₂ . Therefore, it is useful as a catalyst for purifying automobile exhaust gas (particularly diesel engine exhaust gas).

The catalyst (Au—Fe ₂ O ₃ -based catalyst) in which the gold nanoparticles of the present invention are supported on iron oxide includes (1) a step of obtaining an aqueous mixture by mixing a trivalent iron salt and an inorganic alkali component in water. And (2) a step of adding a gold compound to the obtained aqueous mixture to precipitate a precipitate, and (3) a step of firing the obtained precipitate.

Step (1):
In step (1), a trivalent iron salt and an inorganic alkali component are mixed in water to obtain an aqueous mixture. Examples of the trivalent iron salt include nitrate (iron nitrate), sulfate (iron sulfate), and chloride salt (iron chloride) of trivalent iron (Fe (III)), preferably iron nitrate (iron chloride). a _{Fe (NO 3) 3 · 9H} 2 O).

Examples of the inorganic alkali component include alkali metal or alkaline earth metal oxides, hydroxides, carbonates, and the like. Specific examples include MgO, CaO, LiOH, NaOH, KOH, MgO, CaO, Na ₂ CO ₃ , K ₂ CO ₃ , NaHCO ₃ , KHCO _{3 and the} like, preferably Na ₂ CO ₃ , K ₂ CO _3. Alkali metal carbonates such as

  The method for preparing the aqueous mixture containing the trivalent iron salt and the inorganic alkali component is not particularly limited, but the pH when the two are mixed is preferably set in the range of 5 to 11. More preferably, it is pH 7-10, Most preferably, it is pH 8-9. This range is preferable because an iron oxide precursor suitable as a carrier can be formed.

As the method for preparing the aqueous mixture, any method such as a method of mixing an aqueous solution of a trivalent iron salt and an aqueous mixture of an inorganic alkali component, a method of dissolving a trivalent iron salt and an inorganic alkali component in water, etc. can be adopted. . From the simplicity of pH adjustment of the aqueous mixture, it is prepared by adding an inorganic alkali component (particularly Na ₂ CO ₃ , K ₂ CO ₃ or an aqueous solution thereof) to an aqueous solution containing a trivalent iron salt (particularly iron nitrate). preferable. In addition, it is preferable to use distilled water and pure water as water.

The mixing of the aqueous mixture containing the trivalent iron salt and the inorganic alkali component is preferably performed for about 30 minutes to 3 hours at a liquid temperature of 30 to 80 ° C. using the mixing means described above under normal pressure. . Through this mixing process, iron oxide having a well-defined crystal structure is formed, and an Au—Fe ₂ O ₃ -based catalyst having high activity and excellent durability can be obtained by subsequent contact with a gold compound. The mixing means is not particularly limited, and examples thereof include stirring and ultrasonic treatment.

  The concentration of the trivalent iron salt in the aqueous mixture is adjusted to 0.01 to 20 wt%, preferably 0.1 to 15 wt%, more preferably 1 to 10 wt%. Moreover, the density | concentration of the inorganic alkali component in the said aqueous mixture is adjusted to 0.1-20 wt%, Preferably it is 0.5-10 wt%, More preferably, it is adjusted to 1-5 wt%. This range is preferable because it is easy to adjust to the above pH and a suitable iron oxide precursor can be formed.

As a particularly preferable typical example, iron nitrate is used as a salt of trivalent iron, Na ₂ CO ₃ is used as an inorganic alkali component, the iron nitrate concentration in an aqueous solution is 0.1 to 15 wt%, and the Na ₂ CO ₃ concentration is 0.1. As 5-10 wt%, mixing at 30-90 minutes at 50-70 degreeC is mentioned.

Step (2):
In step (2), a gold compound is added to the aqueous mixture obtained in (1) to precipitate a precipitate.

Preferably water-soluble gold salts as the gold _{compound, (0 HAuCl 4 · 4H 2} ) chloroauric acid _Examples, gold chloride, tetrachloroauric (III) ammonium, gold bromide, gold cyanide, gold hydroxide, etc. Is mentioned.

  The method for preparing the aqueous solution of the gold compound is not particularly limited, and the gold compound may be dissolved in water. As the water, distilled water or pure water is preferably used. The concentration of the gold compound in the aqueous solution is 0.01 to 30 wt%, preferably 0.1 to 20 wt%, more preferably 1 to 15 wt%.

  The conditions for adding the aqueous gold compound solution to the aqueous mixture obtained in the above (1) are not particularly limited, but the temperature of the aqueous solution at the time of addition is, for example, about 30 to 80 ° C. You may add and may add in multiple times. After adding an aqueous solution of a gold compound, the mixture is mixed at a liquid temperature of 30 to 80 ° C. for about 10 minutes to 2 hours. As a result, a precipitate is deposited (co-precipitated). This precipitate is washed with water and dried (for example, at about 30 to 200 ° C. for about 3 to 48 hours) to obtain a solid. This is pulverized if necessary and then subjected to step (3).

Step (3):
In step (3), the precipitate obtained in (2) above is fired to obtain an Au—Fe ₂ O ₃ -based catalyst.

  Calcination can be usually performed at a temperature of 100 to 600 ° C., preferably 150 to 400 ° C., more preferably 150 to 250 ° C. under normal pressure and air atmosphere.

Thus, the Au—Fe ₂ O ₃ catalyst of the present invention is produced. The Au—Fe ₂ O ₃ catalyst of the present invention has a structure in which Au nanoparticles are supported on Fe ₂ O ₃ as a support. The amount of Au supported in the catalyst is 0.1 to 10% by weight, preferably 0.1 to 5% by weight.

The average particle diameter of Au nanoparticles on Fe ₂ O ₃ is about 1 to 25 nm. The specific surface area of the Au—Fe ₂ O ₃ -based catalyst is 20 m ² / g or more, preferably 150 m ² / g or more as measured by the BET method.

The form of the Au—Fe ₂ O ₃ -based catalyst can be appropriately selected according to the purpose of use, and examples thereof include powder, granules, pellets, and honeycombs.

The Au—Fe ₂ O ₃ catalyst of the present invention approximates the composition of the Au—Fe ₂ O ₃ catalyst described in Patent Documents 1 to 3, but has a higher activity than the catalysts of Patent Documents 1 to 3. And extremely excellent durability. The reason why the catalyst of the present invention exhibits such excellent properties is not clear at present, but is probably due to a difference in production method.

That is, the catalyst of the present invention is produced through steps (1) to (3) as described above (that is, an aqueous mixture containing ferric nitrate and sodium carbonate is obtained, and chloroauric acid is added thereto). However, the catalysts of Patent Documents 1 and 3 are prepared by adding an aqueous solution of ferric nitrate and chloroauric acid to an aqueous solution of sodium carbonate, and the catalyst of Patent Document 2 is an aqueous suspension of isolated iron oxide. It is produced by adding an aqueous solution of chloroauric acid and an aqueous solution of sodium carbonate to a turbid liquid, and the production method is clearly different. The catalyst according to the present invention takes an unsupported form of gold nanoparticles on an Fe ₂ O ₃ carrier due to such a difference in the production method, leading to higher activity and higher durability. It is thought.

Further, the Au—Fe ₂ O ₃ catalyst of the present invention can oxidize and remove CO from a mixed gas containing hydrogen and CO with high selectivity. Therefore, for example, it is effectively used as a catalyst for removing CO from reformed gas for fuel cells.

Moreover, since the Au—Fe ₂ O ₃ catalyst of the present invention exhibits high catalytic activity with a relatively small amount of supported Au, the amount of expensive Au supported can be reduced and the cost performance is excellent. .

Since the Au—Fe ₂ O ₃ -based catalyst of the present invention has the above-described excellent characteristics, for example, a domestic air purifier, an accessory to a gas water heater (CO removal at the time of incomplete combustion) It is useful as a catalyst for use in gas masks, filters for removing CO from cigarettes, heaters such as heaters and fan heaters (CO removal during incomplete combustion), and the like.

For example, as an example of filter processing, a powdered Au—Fe ₂ O ₃ -based catalyst can be supported on the surface of a substrate via an adhesive or the like to produce a filter. The substrate is not particularly limited as long as it can be used for filters. For example, the material is resin, ceramic, glass, metal, paper, natural fiber, etc., and the structure is nonwoven fabric or mesh. , Honeycombs, sintered bodies, foams, cloths, and the like.

Further, by treating NO, _CO, combustion gas containing O 2, _{N 2} or the like by using the _Au-Fe 2 _{O 3} catalyst of the present invention to reduce NO almost completely in _{N 2 (N 2} O CO can be oxidized almost completely to CO ₂ . Therefore, it is useful as a catalyst for purifying automobile exhaust gas (particularly exhaust gas from a diesel engine), a catalyst for purifying exhaust gas from a thermal power plant, and the like.

The present invention will be described in more detail with reference to examples, but is not limited thereto.
Example 1 (Catalyst of the Present Invention)
An aqueous solution in which 15.17 g of Fe (NO ₃ ) ₃ · 9H ₂ O was dissolved in 100 mL of pure water was immersed in a 60 ° C. water bath, and a 0.3 M Na ₂ CO ₃ aqueous solution was added to adjust the pH to 8.3. Then, after stirring at the same temperature for 1 hour, an aqueous solution (Au 20wt% solution) in which 0.45 g of HAuCl ₄ · 4H ₂ O was dissolved in 100 mL of pure water was added and mixed, and further stirred at the same temperature for 30 minutes to precipitate. Was precipitated.

The precipitate was filtered with a filter paper, and the precipitate on the filter paper was carefully washed with water. This was vacuum dried at 80 ° C. for 12 hours and then calcined at 200 ° C. for 2 hours in an air atmosphere to obtain an Au—Fe ₂ O ₃ catalyst. The amount of gold supported on the catalyst was 3 wt% (from the charged weight).

Even if also slowly dropwise added HAuCl ₄ · 4H ₂ O aqueous solution at a time, little change in the physical properties of the Au-Fe ₂ O ₃ catalyst obtained was not observed.

A TEM photograph of the catalyst obtained in Example 1 is shown in FIG.
[Comparative Example 1]
Add 15.17 g Fe (NO ₃ ) ₃ • 9H ₂ O in 100 mL pure water and 0.45 g HAuCl ₄ • 4H ₂ O in 100 mL pure water (Au 20 wt% solution) This was heated in a 60 ° C. water bath, and 0.3 M Na ₂ CO ₃ aqueous solution was added thereto to adjust the pH to 8.3. The mixture was stirred at the same temperature for 1 hour to precipitate a precipitate.

The precipitate was filtered with a filter paper, and the precipitate on the filter paper was carefully washed with water. This was vacuum dried at 80 ° C. for 12 hours and then calcined at 200 ° C. for 2 hours in an air atmosphere to obtain an Au—Fe ₂ O ₃ catalyst. The amount of gold supported on the catalyst was 3 wt% (from the charged weight).
[Comparative Example 2]
Immerse a 0.3M Na ₂ CO ₃ aqueous solution (pH = 8.3) in a 60 ° C water bath and stir it with 15.17 g Fe (NO ₃ ) ₃ · 9H ₂ O and 0.45 g HAuCl ₄ · 4H ₂ O. An aqueous solution dissolved in 200 mL of pure water was added dropwise to precipitate a precipitate. During the dropwise addition, a 0.3 M Na ₂ CO ₃ aqueous solution was appropriately added to adjust the pH of the aqueous solution to 8.3.

The precipitate was filtered with a filter paper, and the precipitate on the filter paper was carefully washed with water. This was vacuum dried at 80 ° C. for 12 hours and then calcined at 200 ° C. for 2 hours in an air atmosphere to obtain an Au—Fe ₂ O ₃ catalyst. The amount of gold supported on the catalyst was 3 wt% (from the charged weight).

  In addition, the schematic diagram of the manufacturing process in the said Example 1 and Comparative Examples 1 and 2 is shown in FIG.

For the Au-Fe ₂ O ₃ catalyst obtained in the above comparative example, the pore distribution and specific surface area were measured using an automatic specific surface area / pore distribution measuring apparatus (BELSORP-mini, manufactured by Bell Japan Co., Ltd.). did. The pore distribution was calculated based on the BJH method, and the specific surface area was calculated based on the BET method. The results are shown in Table 1.

[Test Example 1] Catalytic activity test (CO oxidation)
0.1 g of powdered catalyst obtained in Example 1 and Comparative Examples 1 and 2 (bulk density = 1.02 g / cm ³ ) was filled into a stainless steel tube having an inner diameter of 4 mm without any gap, and a catalyst-filled tube reactor It was. The flow rates of CO and air were adjusted by a Mass flow controller, and air containing a CO concentration of 500 ppm was supplied to the catalyst packed tube reactor at a flow rate of 60 mL / min. The reaction temperature was changed from room temperature to 200 ° C., and the CO concentration in the reaction gas was quantitatively analyzed by a micro gas chromatograph. The standard reaction conditions were space velocity; SV = 37,000 h ⁻¹ , contact time; W / F = 81.5 kg-cat min mol ⁻¹ . FIG. 3 shows the results of the CO oxidation reaction with each catalyst.

With the catalyst prepared in Example 1, a reaction rate of almost 100% was obtained from room temperature to 200 ° C. On the other hand, it was found that the catalysts prepared according to Comparative Examples 1 and 2 could not obtain a sufficient reaction rate in the temperature range from room temperature to less than 200 ° C. From this, it can be seen that the catalysts of Example 1 and Comparative Examples 1 and 2 have substantially the same pore size, but the CO oxidation activity varies greatly depending on the catalyst preparation conditions. This is thought to be due to the contribution of the Au-supported state on Fe ₂ O ₃ over the surface area and pore diameter of the catalyst.

The reason why the catalyst of Example 1 of the present invention is higher in activity than the catalysts of Comparative Examples 1 and 2 is not clear at present. Probably, the production method of Example 1 is produced by mixing with chloroauric acid in a more ordered state of the crystal structure of iron oxide than the production methods of Comparative Examples 1 and 2. For this reason, in the catalyst of Example 1, it is considered that the gold particles are more supported by the portion where CO is easily chemisorbed (that is, the surface of Fe ₂ O ₃ ) and the activity is high.
[Test Example 2] Selective removal of CO in reformed gas As in Test Example 1, 0.1 g (bulk density = 1.02 g / cm ³ ) of the powdered catalyst obtained in Example 1 above was used as a stainless steel having an inner diameter of 4 mm. The tube was filled without any gaps to obtain a catalyst-filled tube reactor. A tubular reaction filled with catalyst by adjusting the flow rate of the mixed gas of CO, H ₂ and air (hydrogen concentration in the gas 10%) corresponding to the reformed gas composition so that the CO concentration becomes 500 ppm by Mass flow controller. The vessel was supplied at a flow rate of 60 mL / min. The CO concentration in the reaction gas was quantified and analyzed using a micro gas chromatograph. The experiment was conducted at a space velocity SV = 37,000 h ⁻¹ and a contact time W / F = 81.5 kg-cat · min · mol ⁻¹ .

The CO oxidation reaction was examined at a reaction temperature range of 30 to 70 ° C. The results are shown in FIG. From this result, it was shown that the catalyst of Example 1 can selectively oxidize CO in the range of 30 to 70 ° C.
[Test Example 3] CO oxidation and NO reduction Using the catalyst obtained in Example 1 above, a mixed gas containing CO and NO close to the combustion gas composition was treated. Test conditions, test methods and measuring instruments are as follows.
(Test conditions)
Catalyst: Au-supported iron oxide (Au / Fe ₂ O ₃ ) (Example 1)
Catalyst loading concentration: 3wt% (preparation amount)
Catalyst shape: Powder Filled catalyst amount: 0.73 g (bulk density 1.20 g / cm ³ )
Volume occupied by catalyst in the reactor: 0.6 cm ³
Reactor system: Inner diameter 10mm
Test gas: CO approx. 500ppm, O ₂ approx. 7.5%, N ₂ Balance
Measurement temperature: Room temperature (about 24 ℃)
Flow rate: 100 ml / min
SV value: 10,000 / h
(Measuring instrument)
MicroGC “CP-2003” (GL Sciences)
NOx-ANALYZER “ECA-88A” (YANACO)
(Test method)
While adjusting the flow rate from each gas cylinder with a mass flow meter, the test gas was mixed, and the blank gas concentration was measured with a CO measuring device and a NOx measuring device. After heating the thermostat (catalyst) to a predetermined temperature, the test gas was flowed through the apparatus, purged, and then measured with the same measuring device to calculate the removal rate. A schematic diagram of the apparatus is shown in FIG.

The measurement results are shown in FIG. This, at room temperature (24 ° C.), almost completely reduced to _{N 2} and NO _{(N 2} O is not generated), it was found to be almost completely oxidized to CO ₂ and CO. Of course, when the measured temperature is higher than this, higher activity is exhibited.
[Test Example 4] Catalyst durability test (CO oxidation)
Using the catalyst obtained in Example 1 above, a catalyst durability test was performed using the apparatus of Test Example 3.

Test gas: CO about 500 ppm, NO ₂ about 100 ppm, O ₂ about 7.5%, N ₂ Balance was used.

The measurement results are shown in FIG. From this, it was found that CO can be almost completely oxidized to CO ₂ even after 2000 hours at room temperature (24 ° C.). It was revealed that the catalyst obtained in Example 1 maintains high activity for a long time.
[Test Example 5] Comparative Test with Reference Gold Catalyst A comparative test of CO treatment was performed on the catalyst of Example 1 and the reference gold catalyst (Gold reference catalyst Type C, manufactured by Sud Chemie Catalyst Co., Ltd., provided by World Gold Council). As the specifications of the reference gold catalyst, the composition was Au—Fe ₂ O ₃ , and the gold loading was 4.4 wt%. In the test, the apparatus of Test Example 3 was used, but only the volume occupied by the catalyst was set to 1/10 of Test Example 3, that is, 0.06 cm ³ , the other conditions were the same as in Test Example 3, and the space velocity was 10 times SV. The test was conducted at = 100,000 h- ¹ . The catalyst loading was 0.073 g (bulk density = 1.20 g / cm ³ ) for the catalyst of Example 1 and 0.085 g (bulk density = 1.39 g / cm ³ ) for the reference gold catalyst. The test time was 6 hours (360 minutes).

  In this comparative test, the measurement is based on SV, so the amount of catalyst filling differs if the bulk density of the catalyst to be filled is different. In other words, the reference gold catalyst having a bulk density higher than that of the catalyst of Example 1 is subjected to a comparative test under advantageous conditions based on the catalyst loading.

  The results of the catalyst of Example 1 and the reference gold catalyst are shown in FIG. 8 (a) and FIG. 8 (b), respectively.

  From FIG. 8 (a), the catalyst of Example 1 showed a CO removal rate of 90% or more both after opening and after standing in the air for 3 days.

  On the other hand, from FIG. 8 (b), the reference gold catalyst was initially highly active (removal rate 100%) immediately after opening, but deteriorated with time and reached a removal rate of 80% after 6 hours. . In addition, after leaving in the air for 3 days, the removal rate initially showed 30%, and after 6 hours, the removal rate fell below 10%.

From this, it was shown that the catalyst of Example 1 showed very high activity and durability with respect to the existing gold catalyst.
[Test Example 6] High-concentration CO test 0.73 g (bulk density 1.20 g / cm ³ ) of the powdered catalyst of Example 1 was filled into a tube with an inner diameter of 4 mm, and the catalyst was φ4 mm and a cylinder with a height of 4.77 cm. The catalyst packed tube reactor was such that the volume occupied by the catalyst was 0.6 cm ³ . By flowing air containing 5000 ppm of CO into the reactor at a flow rate of 100 ml / min, the space velocity; SV = 10000 hr ⁻¹ , and the CO concentration was measured at the outlet of the reactor. 100%.

Thus, it was found that even at high concentration CO, high CO removal activity was exhibited.
[Test Example 7] Filter processing test The powdery catalyst of Example 1 was supported on a urethane foam nonwoven fabric having a size of 100 mm x 100 mm x 5 mm. As a supporting method, an adhesive was applied to the surface of the nonwoven fabric, and then the catalyst was sprinkled to support the surface of the urethane foam. Excess catalyst was removed, and a catalyst filter in which the catalyst of Example 1 was supported on the urethane foam surface was prepared. The supported amount was 0.75 g / cm ² . This filter was cut into a size of 10 mm in diameter, and this was packed into a tubular reactor having an inner diameter of 10 mm to obtain a catalyst-packed reactor. A catalytic activity test was conducted by feeding a test gas of about 500 ppm CO, about 7.5 ppm O ₂ and N ₂ balance into this reactor at 100 mL / min. The result is shown in FIG.

  From these results, it was shown that even when the catalyst of Example 1 was supported on a non-woven fabric and filtered, it had a normal temperature oxidation activity of CO as in the case of the catalyst powder alone.

The schematic diagram of the manufacturing process of each catalyst of Example 1 and Comparative Examples 1 and 2 is shown. 2 is a TEM photograph of the catalyst of Example 1. 4 is a graph showing the results of activity tests (CO oxidation) of the catalysts of Example 1 and Comparative Examples 1 and 2 in Test Example 1; 6 is a graph showing the result of selective CO removal in the reformed gas of the catalyst of Example 1 in Test Example 2. FIG. 10 is a schematic diagram of an apparatus used in Test Example 3. FIG. 6 is a graph showing the results of a test for treating a mixed gas containing CO and NO using the catalyst of Example 1 in Test Example 3. FIG. 6 is a graph showing the results of a catalyst durability test (CO oxidation) using the catalyst of Example 1 in Test Example 4. The comparative test result of the CO treatment of the catalyst of Example 1 and the reference gold catalyst in Test Example 5 is shown. FIG. 8A shows the result of the catalyst of Example 1, and FIG. 8B shows the result of the reference gold catalyst. The result of the processing test of high concentration CO gas (CO 5000 ppm) in Test Example 6 is shown. The result of the processing test of CO gas (CO 500 ppm) in Test Example 7 is shown.

Claims (12)

  A method for producing a catalyst in which gold nanoparticles are supported on iron oxide, (1) a step of mixing a trivalent iron salt and an inorganic alkali component in water to obtain an aqueous mixture, (2) the obtained aqueous solution The manufacturing method including the process of adding a gold compound to a mixture, and depositing a deposit, and the process of (3) baking the obtained deposit.   The production method according to claim 1, wherein in step (1), an inorganic alkali component is added to an aqueous solution containing a trivalent iron salt, and the pH is adjusted to 5 to 11 and mixed.   The manufacturing method according to claim 1 or 2, wherein in the step (3), the baking temperature is 100 to 600 ° C. The trivalent iron salt is iron nitrate, iron sulfate or iron chloride, and the inorganic alkali component is MgO, CaO, LiOH, NaOH, KOH, MgO, CaO, Na ₂ CO ₃ , K ₂ CO ₃ , NaHCO ₃ or The method according to any one of claims 1 to _3, which is KHCO ₃ and the gold compound is chloroauric acid, gold chloride, tetrachlorogold (III) ammonium, gold bromide, gold cyanide or gold hydroxide.   A catalyst produced by the production method according to claim 1, wherein gold nanoparticles are supported on iron oxide.   A method for removing CO from a gas containing CO using the catalyst according to claim 5.   A method for removing nitrogen oxides from a gas containing nitrogen oxides using the catalyst according to claim 5.   A reformed gas treatment catalyst comprising the catalyst according to claim 2.   A method for removing CO from a reformed gas using the catalyst according to claim 5.   A combustion gas treatment catalyst comprising the catalyst according to claim 5.   A method for removing CO and NO from combustion gas using the catalyst according to claim 5.   A filter formed by supporting the catalyst according to claim 5 on a base material.

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