JP2010058074A - Catalyst for oxidizing formaldehyde, method of producing the same, and method of cleaning air using the same catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide tightly mixed oxides of manganese and cerium for use in a catalyst for oxidizing formaldehyde, which oxides can be produced from cheap raw materials by a simple production apparatus and a simple production method and can clean indoor air by completely oxidizing formaldehyde at a relatively low temperature without using noble metal. <P>SOLUTION: The catalyst for oxidizing formaldehyde includes tightly mixed oxides of manganese and cerium. The tightly mixed oxides of manganese and cerium have an X-ray diffraction peak corresponding to the fluorite-type structure of cerium dioxide as its main peak, and contain manganese in an amount of 10 to 60 mass% on the basis of manganese dioxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a catalyst that oxidizes and decomposes harmful substances such as formaldehyde present in air in an office or a house, an air purification method using the same, and a method for producing the catalyst. Formaldehyde is completely oxidized by this catalyst to become carbon dioxide and water and detoxified.

  With the improvement of the airtightness of offices and residences, there is an increasing interest in removing harmful substances such as formaldehyde, toluene and xylene generated from interior materials such as wall materials and floor materials. In particular, formaldehyde may cause chronic respiratory illness due to long-term inhalation. It is designated as a carcinogen and teratogenic substance by the World Health Organization (WHO), and it is the most dangerous as a substance with strong mutagenicity. In the list of chemicals. Therefore, as measures against sick houses, material manufacturers and housing manufacturers have implemented measures such as reducing the formaldehyde concentration by constructing materials that do not generate formaldehyde or aging the interior of the housing before handing over to the owner after construction. It is. However, the source of formaldehyde is not limited to building materials, but covers a wide range of furniture, curtains, carpets, and smoking, and a technology for efficiently and economically treating indoor low-concentration harmful gases is being sought.

  For the removal method of formaldehyde, adsorbents such as activated carbon, zeolite, molecular sheep, porous clay, activated alumina and silica gel are used, but these adsorbents have a lifetime and are saturated when a certain amount of formaldehyde is adsorbed. As a result, the adsorption performance decreases. Therefore, it is necessary to replace the adsorbent regularly, for example, every several months, and excessive labor and cost are required to maintain the performance.

  The method of decomposing indoor harmful substances and odorous substances such as formaldehyde into odorless and harmless substances using catalyst technology usually requires heating to a temperature of 200 ° C or higher, and generally a method using a precious metal catalyst is used. Are known. As a catalyst that does not use a noble metal, for example, a deodorization catalyst (Patent Document 1) such as Mn / Cu composite oxide prepared by coprecipitation of two or more transition metals, or any one of chromium, iron, cobalt and copper and manganese A manganese composite oxide catalyst such as a deodorizing catalyst composition containing a composite oxide (Patent Document 2) has been proposed. Production of complex oxides such as manganese-based materials requires complicated equipment such as coprecipitation and management of manufacturing processes.

  Recently, as a catalyst for efficiently oxidizing and decomposing formaldehyde at room temperature, a catalyst in which a noble metal is supported on a cerium oxide having oxygen defects by reduction treatment (Patent Document 3), a cerium oxide-zirconium oxide composite oxide, etc. The following gold-supported catalyst (Patent Document 4) is disclosed. The method of oxidizing at room temperature does not require the energy cost for raising the temperature of the gas, but there is a possibility that the processing performance may be deteriorated due to the influence of impurities in the gas and accumulation of by-products. In addition, there are problems that the manufacturing method is complicated by reduction treatment, composite oxide production, and the like, and that a large amount of expensive noble metal is supported, resulting in high catalyst costs.

  Other methods include the photocatalytic method of irradiating titanium oxide with ultraviolet light and the ozone oxidation method of generating ozone using electric discharge. However, the effective technology is due to the low processing efficiency and the effect of ozone on the human body. I can't say that.

JP-A-8-243396 Japanese Patent Laid-Open No. 10-180108 JP 2001-187343 A JP 2004-74069 A

  The present invention has been made to solve the above-described problems, and efficiently removes low-concentration formaldehyde in a room at a relatively low temperature by efficiently oxidizing formaldehyde and completely oxidizing it into carbon dioxide and water. A catalyst and an air cleaning method using the same are provided. Moreover, the manufacturing method of this catalyst is simple and does not require complicated manufacturing equipment.

  In order to solve the above problems, the formaldehyde oxidation catalyst of the present invention contains a manganese-cerium homogeneous mixed oxide, and the manganese-cerium homogeneous mixed oxide corresponds to the fluorite structure of cerium dioxide. The X-ray diffraction peak is a main peak, and manganese is contained in an amount of 10 to 60% by mass in terms of manganese dioxide.

Moreover, the formaldehyde oxidation catalyst of this invention can contain 50-100 mass% of manganese-cerium homogeneous mixed oxides, and 0-50 mass% of refractory inorganic oxides.
Aluminum oxide, titanium oxide, zirconium oxide, zeolite, or titanium-based composite oxide can be used as the refractory inorganic oxide, and in particular, Ti—Si composite oxide, Ti—Zr composite oxide, and Ti—Si—Zr composite. It is preferable to use at least one titanium-based composite oxide selected from oxides.

  Further, in the production of the formaldehyde oxidation catalyst of the present invention, the manganese-cerium dense mixed oxide is obtained by mixing a manganese salt solution with cerium oxide or a precursor of cerium oxide, followed by drying and firing at 300 to 900 ° C. in air. Therefore, a catalyst component having high activity is prepared with a simple manufacturing apparatus, and then a catalyst composition containing a manganese-cerium homogeneous mixed oxide is formed into a predetermined shape by a normal extrusion molding method, and dried and fired. A finished catalyst can be produced.

  In the air cleaning method of the present invention, the formaldehyde oxidation catalyst can be brought into contact with the treatment air at room temperature to 250 ° C. to completely oxidize formaldehyde into carbon dioxide and water.

  The manganese-cerium homogeneous mixed oxide used in the formaldehyde oxidation catalyst of the present invention can be produced with inexpensive raw materials, simple production equipment and production methods, and complete oxidation of formaldehyde at a relatively low temperature without using noble metals. Thus, the indoor air can be purified.

The formaldehyde oxidation catalyst of the present invention contains a manganese-cerium homogeneous mixed oxide, and the manganese-cerium homogeneous mixed oxide is a fluorite having a cerium dioxide crystal peak detected when X-ray diffraction is measured. It has a main peak at a position corresponding to the mold structure, and contains 10 to 60% by mass of manganese in terms of manganese dioxide. In addition, the manganese-cerium homogeneous mixed oxide of the present invention shows almost no diffraction peak derived from manganese oxide when measured by X-ray diffraction, and a crystal peak of cerium dioxide is obtained as a main peak. Represents things.
The crystal structure of the powder sample can be confirmed by measuring the lattice spacing (d value). The measurement conditions for X-ray diffraction were a CuKα radiation source, a voltage of 45 KV, a current of 40 mA, a scanning range of 10 to 90 °, and a scanning speed of 0.198 ° / min. In the measurement result of the manganese-cerium intimate mixed oxide obtained by the present invention, the d value of the main peak is in the range of 3.07 to 3.15, and the cerium dioxide described in the JCPDS (Joint Committee of Powder Diffusion Standards) card is used. It almost coincides with 3.12 which is the d value of the fluorite structure. Moreover, the d value of cerium dioxide described on the card is 3.12, 1.91, 1.63, 2.71, etc. in descending order of relative intensity, and there is a crystal peak at almost the same position other than the main peak. It is detected that the crystal structure of the manganese-cerium dense mixed oxide is almost similar to the cerium dioxide fluorite structure.
Manganese-cerium homogeneous mixed oxide contains manganese in the range of 10 to 60 mass%, preferably 15 to 50 mass%, more preferably 20 to 40 mass% in terms of manganese dioxide. Despite containing manganese at such a high content, it is estimated that manganese oxide is highly dispersed on cerium oxide in an amorphous state because there are almost no diffraction peaks derived from manganese oxide. .
When the content in terms of manganese dioxide is less than 10% by mass, the oxidation rate of formaldehyde becomes insufficient and efficient catalytic treatment becomes impossible, and when it exceeds 60% by mass, the stabilization of manganese becomes insufficient and heat resistance is increased. And this is not preferable because it causes a decrease in poisoning resistance.
In general, the crystal structure of manganese oxide includes MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O _{4 and the} like, and especially MnO ₂ is known as active manganese dioxide and has a strong oxidizing power. ing. However, MnO ₂ is difficult to use in the catalytic combustion method because it easily undergoes a phase change by heat treatment. The manganese-cerium homogeneous mixed oxide obtained by the production method of the present application can only detect a fluorite-type crystal peak of cerium dioxide in the X-ray diffraction measurement even when heat-treated at a high temperature of 900 ° C. It has been found that a significant improvement effect can be obtained. Specifically, only a crystal peak of cerium dioxide is detected by heat treatment at 700 ° C. or lower, but some crystal peaks derived from manganese oxide are detected when the temperature exceeds 700 ° C. Manganese oxide is highly reactive, and it is known that when sulfur compounds are present in the processing gas, it will be transformed into manganese sulfide or manganese sulfate, which tends to cause performance degradation. Manganese oxide is stabilized, and an improvement effect is obtained with respect to sulfur poisoning resistance.
When the manganese-cerium homogeneous mixed oxide of the present invention is heat-treated at 900 ° C. for 5 hours, some crystal peaks of manganese oxide (γMn ₃ O ₄ ) appear. The main peak of γMn ₃ O ₄ is detected at a position where the d value is 2.48 to 2.49, but the relative intensity derived from manganese when the intensity of the main peak of cerium near 3.12 is 100 is 30 or less. And more preferably 20 or less.
The manganese-cerium homogeneous mixed oxide can be produced by a solid phase mixing method, a solid-liquid mixing method, a liquid phase coprecipitation method, a sol-gel method using an alkoxide, or the like. A particularly preferable production method is a solid-liquid mixing method that can produce a highly active homogeneous mixed oxide by using a simple production apparatus using an inexpensive raw material. As a solid-liquid mixing method, a precursor of cerium oxide such as cerium oxide or cerium carbonate is impregnated with an aqueous manganese salt solution such as manganese nitrate, and then dried and fired. By firing at 300 to 900 ° C. in air, manganese-cerium homogeneous mixed oxidation having a specific surface area of 20 to 100 m ² / g can be prepared.
The formaldehyde oxidation catalyst of the present invention may contain a refractory inorganic oxide in addition to the manganese-cerium homogeneous mixed oxide. It is preferable that 50-100 mass% of manganese-cerium homogeneous mixed oxide and 0-50 mass% of refractory inorganic oxides are contained. If the content of the manganese-cerium homogeneous mixed oxide in the catalyst is less than 50%, it is not preferable because sufficient catalytic activity cannot be obtained.
Preferably, the refractory inorganic oxide includes one selected from the group consisting of aluminum oxide, titanium oxide, zirconium oxide, zeolite, and titanium-based composite oxide, and more preferably a titanium-based composite oxide is used. . As the titanium-based composite oxide, it is preferable to use one selected from a Ti—Si composite oxide, a Ti—Zr composite oxide, and a Ti—Si—Zr composite oxide. In particular, Ti-Si composite oxide has a high specific surface area, is chemically and thermally stable, and forms a formaldehyde oxidation catalyst with excellent durability when combined with a manganese-cerium homogeneous mixed oxide. can do. In particular, it is suitable for treating a gas containing a sulfur compound that causes a problem in oxidation treatment at a low temperature. In treating indoor low-concentration formaldehyde, the specific surface area of the Ti—Si composite oxide is preferably 100 m ² / g or more, preferably 150 m ² / g or more.

  Next, a specific method for producing a formaldehyde oxidation catalyst will be described. As described above, the manganese-cerium homogeneous mixed oxide can be produced by a liquid phase coprecipitation method or a sol-gel method, but is preferably produced by a simple solid-liquid mixing method. The solid-liquid mixing method is prepared by mixing either manganese or cerium with a solid raw material and the other as a solution, and preferably using a manganese source as a solid as a cerium source in solution. . Specifically, the manganese of the present invention is prepared by mixing amorphous cerium oxide or a precursor of cerium oxide such as cerium carbonate and cerium hydroxide with an aqueous manganese salt solution such as manganese nitrate, manganese chloride and manganese acetate, followed by drying and firing. -A cerium homogeneous mixed oxidation can be prepared. Firing can be carried out in air at 300 to 900 ° C, preferably 500 to 700 ° C. In particular, it is preferable to use cerium carbonate as a cerium source, which can obtain a porous and dense mixed oxide having a high specific surface area.

  Further, as a method for obtaining a manganese-cerium homogeneous mixed oxide having a higher activity and a fine structure, it is preferable to add an organic acid such as acetic acid, citric acid, maleic acid, malic acid, and succinic acid to the aqueous manganese salt solution. . As the addition amount of the organic acid, it can be impregnated by adding 0.1 to 2 mol, preferably 0.3 to 1.5 mol, more preferably 0.5 to 1 mol with respect to 1 mol of the manganese salt. If the addition amount is less than 0.1 mol, the effect of adding an organic acid cannot be obtained. If the addition amount exceeds 2 mol, a reducing atmosphere is formed during firing, which may adversely affect the properties of the dense mixed oxide. .

  The formaldehyde oxidation catalyst of the present invention is formed by extruding the catalyst composition containing the manganese-cerium homogeneous mixed oxide obtained as described above into a desired shape, followed by drying and firing to obtain a finished catalyst. be able to. The catalyst is preferably calcined in air at 300 to 900 ° C., preferably 400 to 600 ° C. The formaldehyde oxidation catalyst can be in the form of granules, pellets, honeycombs and the like.

  As the catalyst composition, in addition to the manganese-cerium composite oxide, a refractory inorganic oxide such as aluminum oxide, titanium oxide, zirconium oxide, zeolite, or titanium-based composite oxide can be added. If necessary, an organic binder such as starch, an inorganic binder such as silica sol or alumina sol, or a ceramic fiber such as glass fiber can be added as a molding aid. The molding aid is preferably added at 15% or less, preferably 10% or less of the catalyst composition. Furthermore, transition metal oxides such as iron, copper, chromium and silver and noble metal components such as platinum, palladium, rhodium and ruthenium may be added to the catalyst composition as a third component. The third component may be molded in advance supported on either or both of manganese-cerium composite oxide and refractory inorganic oxide, or may be added during molding, or impregnated after molding. It may be supported.

The air cleaning method of the present invention is achieved by bringing a formaldehyde oxidation catalyst into contact with air containing formaldehyde at room temperature to 250 ° C. to completely oxidize formaldehyde into carbon dioxide and water. The treatment temperature is preferably as low as possible from room temperature to 200 ° C, more preferably from room temperature to 150 ° C. The space velocity of the catalyst is processable in 1000~1000000hr ^-1, preferably it is preferred to treat a range of 10000~200000hr ^-1. The formaldehyde oxidation catalyst of the present invention can oxidatively decompose harmful substances and odorous substances such as carbon monoxide, VOC, sulfur compounds and nitrogen compounds in addition to formaldehyde in indoor air.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

(Examples 1-3)
A mixed aqueous solution having a total liquid molar concentration of 0.2 mol / L is prepared by measuring cerium nitrate and manganese nitrate having the manganese oxide content shown in Table 1. While stirring the mixed aqueous solution, ammonia water was gradually added dropwise to adjust to pH = 9. The obtained precipitate was filtered and washed, dried at 150 ° C. overnight, calcined at 500 ° C. for 5 hours, pulverized with a hammer mill, and mixed with manganese-cerium homogeneous mixed oxide by liquid phase coprecipitation method. Obtained. The obtained manganese-cerium homogeneous mixed oxide was subjected to X-ray diffraction measurement at a CuKα radiation source, a voltage of 45 KV, a current of 40 mA, a scanning range of 10 to 90 °, and a scanning speed of 0.198 ° / min. In both cases, a main peak was detected at a position showing the fluorite-type crystal structure of cerium dioxide, and no manganese-derived crystal peak was observed. Table 1 shows the X-ray diffraction measurement results and the specific surface area measured by the BET method.

  Add appropriate amount of water to 95 parts by mass of each manganese-cerium composite oxide obtained above, 5 parts by mass of glass fiber and 3 parts by mass of starch, mix with a kneader, and extrude into 5 mmφ 7 mm long cylindrical pellets. And dried and calcined in air at 500 ° C. for 5 hours to obtain a finished catalyst.

(Examples 4 to 5)
Mixed in powdered cerium carbonate and manganese nitrate solution at the composition ratio shown in Table 1, dried at 150 ° C. overnight, then fired at 500 ° C. for 5 hours and then mixed with manganese and cerium by a solid-liquid mixing method. I got a thing. Table 1 shows the physical property measurement results of each of the obtained manganese-cerium homogeneous mixed oxides. Thereafter, the finished catalyst having the composition ratio shown in Table 2 was obtained in the same manner as in Example 1.

(Examples 6 to 7)
In each of Examples 4 and 5, each manganese-cerium soot having the physical properties shown in Table 1 was obtained in the same manner as in Examples 4 and 5, except that 1.0 mol of citric acid was added to the manganese nitrate aqueous solution per mol of manganese. A mixed oxide was obtained. Thereafter, the finished catalyst having the composition ratio shown in Table 2 was obtained in the same manner as in Example 1.

(Examples 8 to 9)
First, a Ti—Si composite oxide (Ti / Si molar ratio = 85/15) was prepared by the following method. After adding 21.3 kg of SNOWTEX-20 (silica sol manufactured by Nissan Chemical Co., Ltd., containing about 20% by weight of SiO ₂ ) to 700 liters of 10% by weight aqueous ammonia, stirring and mixing, a sulfuric acid solution of titanyl sulfate (TiO ₂₎ (125 g / liter, sulfuric acid concentration 550 g / liter) was gradually added dropwise with stirring. The obtained gel was allowed to stand for 3 hours, filtered, washed with water, and then dried at 150 ° C. for 10 hours. This was fired at 500 ° C., further pulverized using a hammer mill, and classified by a classifier to obtain a powder having an average particle diameter of 10 μm. The obtained powder has a specific surface area of 162 m ² / g, and X-ray diffraction measurement does not show any obvious intrinsic peaks of TiO ₂ or SiO ₂ , and Ti having an amorphous microstructure due to a broad diffraction peak. It was confirmed that a —Si composite oxide was formed.

  The Ti-Si composite oxide and the manganese-cerium dense mixed oxide obtained in Examples 6 and 7 were blended in the catalyst composition ratios shown in Table 2, respectively, and the finished catalyst was obtained in the same manner as in Example 1 below. It was.

(Comparative Examples 1-2)
A manganese-cerium mixed oxide of a comparative example was obtained in the same manner as in Example 4 except that the mixing ratio of Mn / Ce in Example 4 was changed to the composition shown in Table 1, and the physical property measurement results are shown in Table 1. Thereafter, a comparative catalyst having a catalyst composition ratio shown in Table 2 was obtained in the same manner as in Example 4.

(Comparative Example 3)
The Ti—Si composite oxide obtained in Example 8 was impregnated with manganese nitrate, dried at 150 ° C. and then fired in air at 500 ° C. for 2 hours to contain 20% by mass of manganese oxide in terms of manganese dioxide. Table 1 shows the physical property measurement results. 95 parts by mass of the powder, 5 parts by mass of glass fiber, and 3 parts by mass of starch were mixed with an appropriate amount of water, extruded in the same manner as in Example 1, dried and then calcined at 500 ° C. for 5 hours to prepare a comparative catalyst. Obtained.

（ホルムアルデヒド分解試験）
実施例１〜９および比較例１〜３で得られた各触媒を用いて、以下の手順でホルムアルデヒド分解試験を実施した。

(Formaldehyde decomposition test)
Using the respective catalysts obtained in Examples 1 to 9 and Comparative Examples 1 to 3, a formaldehyde decomposition test was performed according to the following procedure.

A glass tube having an inner diameter of 15 mm was filled with 25 cc of pellet catalyst, air containing formaldehyde at 1000 ppm and water content of 2.5% was passed at a space velocity of 15000 hr ⁻¹ , and the carbon dioxide concentration at the outlet was measured. The formaldehyde oxidation performance was determined. The performance test results measured at a gas temperature of 40 to 200 ° C. are shown in Table 2.

（熱エージング試験）
実施例１、実施例４、実施例６、実施例９および比較例２の触媒ペレットを電気炉にて空気中９００℃５時間の熱エージングを実施した。熱エージング後にＸ線回折を測定した結果、酸化セリウムの蛍石型以外に酸化マンガン（γＭｎ_３Ｏ_４）に由来するピークがいずれの試料からも検出された。表３にｄ値３．１２近辺のＣｅの主ピークを１００として、ｄ値が２．４８近辺に見られるＭｎの主ピークの相対強度を示した。また反応温度２００℃とした以外は前記ホルムアルデヒド分解試験と同様にして性能試験を実施し結果を表３に示した。

(Thermal aging test)
The catalyst pellets of Example 1, Example 4, Example 6, Example 9 and Comparative Example 2 were subjected to thermal aging at 900 ° C. for 5 hours in air in an electric furnace. As a result of measuring X-ray diffraction after thermal aging, a peak derived from manganese oxide (γMn ₃ O ₄ ) was detected in any sample in addition to the cerium oxide fluorite type. Table 3 shows the relative intensity of the main peak of Mn that is observed around the d value of 2.48, where the main peak of Ce near the d value of 3.12 is 100. Further, a performance test was carried out in the same manner as the formaldehyde decomposition test except that the reaction temperature was 200 ° C., and the results are shown in Table 3.

以上の結果より本発明のホルムアルデヒド酸化触媒により、高価な貴金属を使用しなくても比較的緩和な条件で室内空気の清浄化が行える。また実施例の触媒は熱エージングに対して優れた耐久性を有しており、長期使用が可能であると考えられる。

From the above results, the formaldehyde oxidation catalyst of the present invention can clean indoor air under relatively mild conditions without using expensive noble metals. Moreover, the catalyst of an Example has the outstanding durability with respect to heat aging, and it is thought that it can be used for a long term.

It is a graph which shows the formaldehyde decomposition | disassembly performance in each temperature conditions of this invention catalyst and a comparison catalyst.

  The present invention relates to a technique for oxidatively decomposing harmful substances such as formaldehyde present in the air of an office or a house, and can be used in an air cleaning method.

Claims (6)

A formaldehyde oxidation catalyst containing a manganese-cerium homogeneous mixed oxide, wherein the manganese-cerium homogeneous mixed oxide has an X-ray diffraction peak corresponding to a fluorite structure of cerium dioxide as a main peak. And formaldehyde oxidation catalyst characterized by containing 10-60 mass% of manganese in conversion of manganese dioxide. The formaldehyde oxidation catalyst according to claim 1, wherein the formaldehyde oxidation catalyst contains 50 to 100 mass% of the manganese-cerium homogeneous mixed oxide and 0 to 50 mass% of the refractory inorganic oxide. The formaldehyde oxidation catalyst according to claim 2, wherein the refractory inorganic oxide contains at least one selected from the group consisting of aluminum oxide, titanium oxide, zirconium oxide, zeolite, and titanium-based composite oxide. The formaldehyde oxidation catalyst according to claim 3, wherein the titanium-based composite oxide includes at least one selected from a Ti-Si composite oxide, a Ti-Zr composite oxide, and a Ti-Si-Zr composite oxide. A method for producing a formaldehyde oxidation catalyst according to claims 1 to 4, wherein a manganese salt solution is mixed with cerium oxide or a precursor of cerium oxide, dried and then calcined in air at 300 to 900 ° C to make manganese-cerium compact. The manufacturing method of the formaldehyde oxidation catalyst obtained by preparing mixed oxide, extruding the catalyst composition containing this manganese-cerium homogeneous mixed oxide, and drying and baking. An air cleaning method in which the formaldehyde oxidation catalyst according to claim 1 is brought into contact with air containing formaldehyde at room temperature to 250 ° C to completely oxidize formaldehyde into carbon dioxide and water.

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