JP2007244974A - Nox gas adsorbing/decomposing agent and method for manufacturing the same, and method for adsorbing and decomposing nox gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NOx gas adsorbing/decomposing agent that efficiently adsorbs and decomposes an NOx gas contained in the atmosphere or the like, a method for easily manufacturing the same, and a method for adsorbing and decomposing the NOx gas. <P>SOLUTION: The manufacturing method is to polycondense a sol body obtained by hydrolyzing an inorganic alkoxide in the sol-gel process into a gel body obtained in the presence of a carbonate and/or hydroxide of an alkaline earth metal and impregnate a photocatalyst precursor solution to the gel body, and heat and sinter the solution. This allows the NOx gas adsorbing/decomposing agent with a surface of the oxide of the alkaline earth metal scattered in a porous material coated with the photocatalyst to be provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an adsorption / decomposition agent excellent in adsorption / decomposition performance of nitrogen oxide gas and sulfur oxide gas contained in the atmosphere, a method for producing the same, and a NO _x gas adsorption / decomposition method.

Consumption of fossil fuel increases with increasing standard of living, nitrogen oxides (hereinafter, referred to as NO _x) sulfur oxides not only gas (hereinafter, referred to as SO _x) gas and carbon monoxide, two more Pollution caused by oxidants and dioxins is a problem as secondary air pollution.

In recent years, research and development regarding a method for removing a specific acid gas such as NO _x and SO _x and a catalyst have been actively performed. For example, attempts have been made to decompose and purify harmful substances, particularly NO _x gas, using the reducing power of electrons generated by photoexcitation of a photocatalyst such as titanium oxide or the oxidizing power of holes. Attempts have also been made to support metals such as V, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pt, Pd, and Ag or compounds of the metals on the surface of photocatalytic particles such as titanium oxide. However, these techniques have a problem that a sufficient photocatalytic function cannot be achieved.

Thus, Patent Document 1 contains a photocatalyst for removing nitrogen oxides, which comprises carrying a rare earth metal compound by neutralization on the surface of the photocatalyst particle, and the photocatalyst particle and an alkaline earth metal compound. A photocatalyst for removing nitrogen oxide is disclosed. This nitrogen oxide removing photocatalyst has advantages in that the rare earth metal compound is firmly supported on the particle surface, so that the ability to remove harmful substances by the photocatalyst is improved and the photocatalytic function lasts for a long period of time.
JP 10-174881 A (published June 30, 1998)

  However, in the technique disclosed in Patent Document 1, it is necessary to carry a rare earth metal compound and an alkaline earth metal compound again after manufacturing photocatalyst particles such as titanium oxide in advance, so that the manufacturing process is complicated. There is.

The present invention, which was made in order to solve the above problems, its object is efficiently adsorb and decompose NO _x gas adsorption decomposing agent NO _x contained in the atmosphere moderate, and it easily And a NO _x gas adsorption decomposition method.

The inventors of the present application added an alkaline earth metal compound to a sol obtained by hydrolyzing an inorganic alkoxide, mixed uniformly, and then prepared a gel by a polycondensation reaction to obtain a porous material. a photocatalyst component impregnation of the photocatalyst by heat treatment, by heating firing, even at low temperatures, found that it is possible to obtain an outdoor, efficiently removed can photocatalyst NO _x gases in the atmosphere such as indoors, the The invention has been completed.

That is, in order to solve the above problems, the NO _x gas adsorption / decomposition agent according to the present invention has an alkaline earth metal oxide dispersed in a porous material, and a photocatalyst is formed on at least a part of the surface of the oxide. It is characterized by adhering.

In the NO _x gas adsorption / decomposition agent according to the present invention, the porous material is preferably silica gel.

In the NO _x gas adsorption / decomposition agent according to the present invention, the photocatalyst is preferably titanium oxide.

In the NO _x gas adsorption / decomposition agent according to the present invention, the alkaline earth metal is preferably magnesium or calcium.

In addition, in order to solve the above-described problem, the method for producing an NO _x gas adsorption / decomposition agent according to the present invention comprises converting a sol body obtained by hydrolyzing an inorganic alkoxide solution by a sol-gel method, and converting an alkaline earth metal carbonate to A gel body obtained by polycondensation in the presence of a salt and / or hydroxide is impregnated with a photocatalyst precursor solution and heated and fired.

In the method for producing an NO _x gas adsorption / decomposition agent according to the present invention, it is preferable that the gel body impregnated with the photocatalyst precursor solution has a particle shape.

The manufacturing method of the NO _x gas adsorption decomposing agent according to the present invention, as the inorganic alkoxide, it is preferable to use alkoxide of silicon.

The manufacturing method of the NO _x gas adsorption decomposing agent according to the present invention, as alkoxide of the silicon, it is preferred to use tetraethoxysilane (also referred to as ethyl silicate).

The manufacturing method of the NO _x gas adsorption decomposing agent according to the present invention, as the alkaline earth metal, it is preferable to use magnesium or calcium.

The manufacturing method of the NO _x gas adsorption decomposing agent according to the present invention, as the photocatalyst precursor solution, it is preferable to use a tetraisopropyl titanate.

The present invention also includes a NO _x gas adsorption / decomposition agent produced by the production method described above.

Further, NO _x gas adsorption decomposition method according to the present invention, the above of the NO _x gas adsorption decomposer, by contacting the NO _x gas, adsorbing the NO _x gases to the NO _x gas adsorption decomposer, and said The NO _x gas is decomposed by a photocatalyst.

As described above, in the NO _x gas adsorption / decomposition agent according to the present invention, the alkaline earth metal oxide is scattered in the porous material, and the photocatalyst is attached to at least a part of the surface of the oxide. It is characterized by that. Further, NO _x gas adsorption decomposition method according to the present invention, the above of the NO _x gas adsorption decomposer, by contacting the NO _x gas, adsorbing the NO _x gases to the NO _x gas adsorption decomposer, and said The NO _x gas is decomposed by a photocatalyst.

According to the above configuration, the photocatalyst action and the adsorbing action are obtained by the presence of the photocatalyst on the surface of the alkaline earth metal in the porous material that is basic by supporting the alkaline earth metal oxide. since occurs in very close positions, it is possible to efficiently adsorb and decompose NO _x gases are harmful substances contained in the atmosphere moderate. For example, in the case of the NO _x gas adsorption decomposing agent using titanium oxide as the photocatalyst, it is possible to oxidize and decompose NO _x gas adsorbed by the titanium oxide.

In addition, as described above, the method for producing an NO _x gas adsorption / decomposition agent according to the present invention comprises converting a sol body obtained by hydrolyzing an inorganic alkoxide solution by a sol-gel method to an alkaline earth metal carbonate and / or Alternatively, the gel body obtained by polycondensation in the presence of a hydroxide is impregnated with a photocatalyst precursor solution and heated and fired.

As a result, NO _x gas, which is a harmful substance contained in the atmosphere, can be efficiently adsorbed and decomposed to a basic gel body carrying an alkaline earth metal, and the alkaline earth metal. A NO _x gas adsorption / decomposition agent with high adsorption / decomposition performance that can decompose the adsorbed NO _x gas by the photocatalyst present on the surface of the catalyst can be produced by a simple method.

Specifically, a porous gel body can be obtained by polycondensation of the sol body in the presence of an alkaline earth metal carbonate and / or hydroxide, and the gel body (NO _x gas) Since the specific surface area of the adsorption / decomposition agent can be increased, the adsorption resolution can be improved.

  Moreover, according to the present invention, a high photocatalytic function can be realized with a small number of photocatalysts by adopting a configuration in which the photocatalyst is attached to the surface of the alkaline earth metal. Therefore, for example, the amount of use (addition) of the photocatalyst can be reduced as compared with a configuration in which the photocatalyst is attached to the entire surface of the porous gel body or a configuration in which the photocatalyst is dispersed in the gel body. .

The inventors of the present invention previously used an acidic gas adsorption decomposition obtained by hydrolyzing an inorganic alkoxide mixture containing an alkoxide of an alkaline earth metal and an alkoxide of a metal other than an alkali metal by a sol-gel method and performing condensation polymerization. A patent application has been filed for the agent (Japanese Patent Laid-Open No. 11-76814 (published March 23, 1999)). Therefore, the inventors of the present application have made extensive studies to develop an adsorption / decomposition agent that further enhances the adsorption / decomposition performance for NO _x gas among acid gases, and as a result, dispersed alkaline earth metal in the porous material, By coating at least a part of the surface of the alkaline earth metal with a photocatalyst, it is found that an acid gas adsorption / decomposition agent that realizes high adsorption / decomposition performance compared to the previous acid gas adsorption / decomposition agent can be obtained, The present invention has been reached.

Hereinafter, NO _x gas adsorption decomposing agent according to the present invention, and an embodiment of its manufacturing method will be described. In the following description, various technically preferable limitations for carrying out the present invention are given, but the scope of the present invention is not limited to the following embodiments.

[1] NO _x gas adsorption decomposer NO _x gas adsorption decomposing agent according to the present invention, at least a portion of said alkaline earth metal surface in the porous material the alkaline earth metal is scattered photocatalyst adheres Yes.

  Hereinafter, the porous material in which the alkaline earth metal is dispersed and the photocatalyst will be described in detail.

(1-a) Porous material interspersed with alkaline earth metal The porous material interspersed with alkaline earth metal used in the present embodiment is a sol body obtained by hydrolyzing an inorganic alkoxide solution by a sol-gel method. Is a gel obtained by polycondensation in the presence of an alkaline earth metal carbonate and / or hydroxide.

Here, the inorganic alkoxide is an alkoxide other than an alkaline earth metal, and has a general formula: M (OR) _m (where M is Li, Na, Cu, Zn, B, Al, Ga, Y, It is at least one element selected from the group consisting of Si, Ge, Ta, W, La, Nd, Ni, Zr and Ti, and R is an alkyl group, preferably a lower alkyl group having 1 to 4 carbon atoms. And m is an integer corresponding to the valence of M). Specific examples of alkoxides other than alkaline earth metals are listed below.

(I) Alkoxysilane When M is Si (valence: 4), it is represented by Si (OR) ₄ . Examples of such alkoxysilane include Si (OCH ₃ ) ₄ and Si (OC ₂ H ₅ ) ₄ . Of these, Si (OC ₂ H ₅ ) ₄ is preferable.

(B) Aluminum alkoxide When M is Al (valence: 3), it is represented by Al (OR) ₃ . Examples of such aluminum alkoxide include Al (OCH ₃ ) ₃ , Al (OC ₂ H ₅ ) ₃ , Al (On-C ₃ H ₇ ) ₃ , Al (Oi-C ₃ H ₇ ) ₃ , al _{(OC 4} H _{9) 3} and the like.

(C) Titanium alkoxide When M is Ti (valence: 4), it is represented by Ti (OR) ₄ . Examples of such a titanium alkoxide include Ti (OCH ₃ ) ₄ , Ti (OC ₂ H ₅ ) ₄ , Ti (OC ₃ H ₇ ) ₄ , Ti (OC ₄ H ₉ ) ₄ , and Ti (Oi-C _3). H ₇ ) _{4 and the} like.

(D) Zirconium alkoxide When M is Zr (valence: 4), it is represented by Zr (OR) ₄ . Examples of such zirconium alkoxide include Zr (OCH ₃ ) ₄ , Zr (OC ₂ H ₅ ) ₄ , Zr (Oi-C ₃ H ₇ ) ₄ , Zr (Ot-C ₄ H ₉ ) ₄ , _{Zr (O-n-C 4} H 9) 4 , and the like. Of these, Zr (OC ₃ H ₇ ) ₄ and Zr (Ot—C ₄ H ₉ ) ₄ are preferable.

As (e) Other alkoxides other _{alkoxides, Fe (OC 2 H 5)} 3, V (O-i-C 3 H 7) 4, Sn (OC 2 H 5) 4, Sn (O-i-C 4 _{H 9) 4, Sn (O} -t-C 4 H 9) 4, Li (OC 2 H 5) 3, Be (OC 2 H 5) 3, B (OC 2 H 5) 3, P (OC2H5) 3 , P (OCH ₃ ) _{3 and the} like. _{Further, Ni [Al (O-i} -C 3 H 7) 4] 2 , and the like as a bimetallic alkoxide.

Among the above, alkoxysilane (silicon alkoxide) is most preferable. By using alkoxysilane, a porous gel can be realized. That is, a wide specific surface area of the gel body can be secured. Therefore, it is possible to improve the adsorption decomposition efficiency of the NO _x gases. Moreover, since the gel body excellent in light transmittance can be realized by using alkoxysilane, the catalytic activity of the photocatalyst adhered to the alkaline earth metal can be improved. In addition, the heat resistance of the NO _x gas adsorption / decomposition agent can be increased.

  In addition, the inorganic alkoxide contained in the inorganic alkoxide solution may include a plurality of kinds of the above-described various alkoxides, or may include only one kind.

  The sol obtained by hydrolyzing the inorganic alkoxide solution as described above is subjected to polycondensation in the presence of an alkaline earth metal carbonate and / or hydroxide, whereby an alkaline earth metal is contained in the gel. It becomes a gel body in which the oxides are scattered.

The specific kind of the alkaline earth metal is not particularly limited, and any of Group IIA elements can be preferably used. In the present invention, among the Group IIA elements, magnesium (Mg) And calcium (Ca) can be particularly preferably used. Therefore, alkaline earth metal hydroxides and / or carbonates include magnesium carbonate (MgCO ₃ ), calcium carbonate (CaCO ₃ ), magnesium hydroxide (Mg (OH) ₂ ), calcium hydroxide (Ca (OH ) At least any one of ₂ ) can be used particularly preferably. By adding these, oxides such as CaO and / or MgO are formed in the porous material. Thereby, the alkaline earth metal oxide acts as a strong base point, and can improve the NO _x gas adsorption decomposition performance.

(1-b) Photocatalyst In the NO _x gas adsorption / decomposition agent in the present embodiment, a photocatalyst is present on the surface of the alkaline earth metal scattered in the porous material.

Although the details of the method for producing the NO _x gas adsorption / decomposition agent will be described later, in the present invention, the porous material in which the alkaline earth metal is dispersed is impregnated with the photocatalyst precursor solution and heated and fired to thereby produce the alkali. The surface of the earth metal is coated with a photocatalyst. As the photocatalyst to be coated, those having a conventionally known photocatalytic action can be used. For example, titanium oxide, zinc oxide, and tungsten oxide can be used.

  For example, when titanium oxide is used as a photocatalyst, tetraisopropyl titanate, tetrabutyl titanate, butyl titanate dimer, tetrakis (2-ethyl) obtained by reaction of titanium tetrachloride or metal titanium with alcohol, etc. as a photocatalyst precursor solution. Hexyloxy) titanium, tetrastearyl titanate, triethanolamine titanate, diisopropoxy bis (acetylacetonato) titanium, dibutoxy bis (triethanolaminato) titanium, titanium ethyl acetoacetate, titanium isopropoxy octylene glycolate, Titanium alkoxides such as titanium lactate, and isopropyltriisostearoyl titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropylate Sus (dioctylpyrophosphate) titanate, Tetraisopropylbis (dioctylphosphite) titanate, Tetraoctylbis (ditridecylphosphite) titanate, Tetra (2,2-diallyloxymethyl-1-butyl) bis (ditridecyl) phosphite titanate , Titanate cups such as bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate, isopropyltri (dioctylphosphate) titanate, isopropyltricumylphenyl titanate, isopropyltri (N-amidoethylaminoethyl) titanate An organic titanium-containing solution such as a ring agent can be used. However, the present invention is not limited to this.

  When zinc oxide is used as a photocatalyst, zinc oxalate, zinc carbonate, zinc acetate, various alkoxides (zinc methoxide, zinc ethoxide, zinc isopropoxide, zinc butoxide), bis (acetylethylacetonate) zinc, ethylacetate A zinc oxide-containing solution such as acetate can be used. However, the present invention is not limited to this.

In addition, when tungsten oxide is used as a photocatalyst, tungsten trioxide, tungstic acid, calcium tungstate, and the above titanium-containing solution can be used alone or in a mixture without limitation, but the concentration is not limited thereto. You may dilute with a compatible solvent for adjustment. The diluent is limited to any one that is compatible with a titanium-containing solution such as ethanol, 1-propanol, 2-propanol, N-hexane, benzene, toluene, xylene, trichlene, propylene dichloride, and water, either alone or as a mixture. It is available without.

[2] Method for producing NO _x gas adsorption / decomposition agent The present invention relates to a sol obtained by hydrolyzing an inorganic alkoxide solution by a sol-gel method, and the presence of an alkaline earth metal carbonate and / or hydroxide. the gel body obtained by polycondensation below, to produce a NO _x gas adsorption decomposer by heating calcined impregnated with a photocatalyst precursor solution.

(2-a) Hydrolysis of alkoxide The concentration of the alkoxide of a metal other than the alkaline earth metal used as the inorganic alkoxide in the solution is preferably 300 to 500 g / L. The hydrolysis temperature is preferably 20 to 85 ° C.

(2-b) Solation When a sol-gel method catalyst is added to the hydrolyzed inorganic alkoxide as necessary and stirred for 0.5 to 2 hours, the hydrolysis is substantially completed, and the reaction solution is sol or precipitate. , Become an emulsion. Examples of the sol-gel method catalyst include an acid catalyst and a base catalyst, and it is preferable to use them together.

  The acid catalyst is used for the hydrolysis reaction of inorganic alkoxide. When the reaction solution is vigorously stirred during the hydrolysis, carbon dioxide in the air is taken in to generate carbonic acid, which acts as an acid catalyst. Therefore, it is not necessary to add an acid catalyst. Specific acid catalysts include mineral acids such as hydrochloric acid, sulfuric acid and nitric acid, mineral acid anhydrides such as hydrogen chloride gas, tartaric acid, phthalic acid, maleic acid, dodecyl succinic acid, hexahydrophthalic acid, methyl nadic acid, Pyromellitic acid, benzophenone tetracarboxylic acid, dichlorosuccinic acid, chlorendic acid, phthalic anhydride, maleic anhydride, dodecyl succinic anhydride, hexahydrophthalic anhydride, methyl nadic anhydride, pyromellitic anhydride, benzophenone tetra Examples thereof include organic acids such as carboxylic acid, dichlorosuccinic anhydride, chlorendic anhydride, and anhydrides thereof.

  The amount of the acid catalyst to be used is preferably 0.001 to 0.5 mol, particularly preferably 0.005 to 0.3 mol, per 1 mol of the inorganic alkoxide. If the amount is less than 0.001 mol, hydrolysis may be insufficient. If the amount exceeds 0.5 mol, the polycondensation reaction proceeds excessively, and the viscosity may increase excessively.

  The base catalyst mainly acts not only as a catalyst for polycondensation reaction of the hydrolysis product of inorganic alkoxide, but also as a catalyst for rapid crosslinking reaction and formation of a three-dimensional network structure. The base catalyst may be either an inorganic base or an organic base. Examples of the inorganic base include calcium hydroxide, potassium hydroxide, sodium hydroxide, lithium hydroxide, rubidium hydroxide, magnesium hydroxide, ammonia and the like. Examples of the organic base include primary amines, secondary amines, tertiary amines, polyamines, and amine complexes. Specific examples of organic bases include ethylenediamine, diethylenetriamine, ethanolamine, butylamine, triethylenetetramine, diethylaminopropylamine, N-aminoethylpiperazine, N, N-dimethylbenzylamine, tripropylamine, tributylamine, tripentylamine, tris (Dimethylaminomethyl) phenol, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, polyamide resin, dicyandiamide, boron trifluoride / monoethylamine, menthanediamine, xylylenediamine, ethylmethylimidazole and the like. Of the basic catalysts, tertiary amines that are substantially insoluble in water and soluble in organic solvents (for example, N, N-dimethylbenzylamine, tripropylamine, tributylamine, tripentylamine, etc.) and ammonia are more preferred, N, N-dimethylbenzylamine and ammonia are particularly preferred. In particular, when ammonia gas is used, a fine particulate porous material can be obtained.

  It is preferable that the usage-amount of a base catalyst is 0.002-1.5 mol with respect to 1 mol of inorganic alkoxides. If it is less than 0.002 mol, the polycondensation reaction proceeds slowly, and if it exceeds 1.5 mol, the polycondensation reaction proceeds rapidly, so that the resulting porous material may be non-uniform. When a tertiary amine that is insoluble in water and soluble in an organic solvent is used as the base catalyst, the amount used is preferably 0.004 to 0.008 mol. In the case of other than tertiary amine, the amount is preferably 0.1 to 1.5 mol.

(2-c) Solvent As a solvent for hydrolysis, a mixed solvent of water necessary for hydrolysis and an organic solvent soluble in water can be used. As the organic solvent, methanol, ethanol, butanol, propanol, pentanol, hexanol, acetone, methyl ethyl ketone, and formamide are preferable.

The usage-amount of water is 10 mol or less with respect to 1 mol of inorganic alkoxides, Preferably it is 1-10 mol, More preferably, it is 2-8 mol, Most preferably, it is 3-7 mol. If the amount of water used is too small, hydrolysis of the alkoxide is slow and the condensation reaction is difficult to proceed. However, it is not always necessary to add water to the solvent because hydrolysis proceeds gradually with moisture in the air. In particular, when using a highly hygroscopic alkoxide containing zirconium or the like, it is not necessary to add water. If the amount of water exceeds 10 mol, the NO _x gas adsorption / decomposition characteristics of the obtained porous material are deteriorated, which is not preferable.

(2-d) Addition of hydroxide and / or carbonate of alkaline earth metal Alkaline earth metal hydroxide and / or carbonate may be added before hydrolyzing the inorganic alkoxide by the sol-gel method or Any of the latter may be used, but after hydrolysis is preferred.

  As the addition amount of the alkaline earth metal hydroxide and / or carbonate, the blending ratio A: B (atomic ratio) of the inorganic alkoxide (A) and the alkaline earth metal (B) is 100: 1. What is necessary is just to add so that it may become -1: 1, It is preferable that it is 50: 1-2: 1, and 20: 1-3: 1 is the most preferable. If the addition amount of the alkaline earth metal is further smaller than the blending ratio of 100: 1, the formation of the base point becomes insufficient, such being undesirable. Further, if the amount of the alkaline earth metal added is larger than the blending ratio of 1: 1, the specific surface area decreases and the adsorptive decomposition action is insufficient, which is not preferable.

  In addition, when adding an alkaline earth metal hydroxide, the above-described base catalyst may not be added.

(2-e) Gelation by polycondensation reaction Polycondensation reaction of hydrolysis product (sol, precipitate or emulsion) of inorganic alkoxide in the presence of hydroxide and / or carbonate of alkaline earth metal As it progresses, gelation occurs. The gelation time can be freely adjusted in the range of several seconds to several hours depending on the amount of the base catalyst. When the pH of the sol-like mixture is adjusted to about 6 to 8 and the amount of the base catalyst is small, the gelation time becomes as long as several hours. The polycondensation temperature is preferably 20 to 85 ° C.

(2-f) Drying The gel obtained by condensation polymerization is pulverized and dehydrated by heating for 1 to 8 hours at a temperature of 200 ° C. or lower, preferably 100 to 180 ° C., particularly 120 to 150 ° C. A gel-like body is obtained.

(2-g) Addition of photocatalyst The fine-particle gel after drying is immersed in the photocatalyst precursor solution described above.

  The amount of the photocatalyst precursor in the photocatalyst precursor solution is such that the mixing ratio B: C (atomic ratio) between the alkaline earth metal (B) added in (2-d) and the photocatalyst precursor (C) is as follows. And a solution containing an amount of 100: 1 to 2.5: 1, preferably 50: 1 to 10: 1, and more preferably 30: 1 to 15: 1. . If the amount of the photocatalyst precursor is further smaller than the mixing ratio of 100: 1, it is not preferable because a desired photocatalytic action cannot be obtained. Further, if the amount of the photocatalyst precursor is larger than the blending ratio of 2.5: 1, the photocatalyst precursors are aggregated and cannot fully exhibit the photocatalytic action, which is not preferable.

  The immersion time may be, for example, 5 minutes to 5 hours, preferably 2 to 3 hours, and the immersion temperature may be 20 to 50 ° C., preferably 20 to 30 ° C. However, it is not limited to these.

(2-h) Drying and calcination The particulate gel body immersed in the photocatalyst precursor solution is finally dried and baked to become a NO _x gas adsorption / decomposition agent.

  The drying is performed by heat dehydration at a temperature of 200 ° C. or lower, preferably 100 to 180 ° C., particularly 120 to 150 ° C. for 1 to 8 hours, as in (2-f) above.

  In the firing, alkaline earth metal oxides such as MgO and CaO are formed in a porous material (gel body) from at least a part of the alkaline earth metal carbonate and / or hydroxide, and at least the photocatalyst precursor. The reaction is carried out under such a condition that a part becomes a photocatalyst. Note that when an alkaline earth metal alkoxide is used as the inorganic alkoxide, an alkaline earth metal oxide is also generated from the alkaline earth metal alkoxide. As firing conditions, for example, the firing temperature can be 400 to 800 ° C., and preferably 600 to 800 ° C. The firing time can be 0.5 to 20 hours, and preferably 4 to 15 hours.

The NO _x gas adsorption / decomposition agent produced by the above production method has a basic porous material due to the alkaline earth metal supported thereon, so NO _x which is a harmful substance contained in the atmosphere or the like. Gas can be adsorbed and decomposed efficiently. Further, since the photocatalyst is present on the surface of the alkaline earth metal, the adsorbed NO _x gas can be efficiently decomposed. For example, in the case of the NO _x gas adsorption decomposing agent using titanium oxide to the photocatalyst, it is possible to oxidize and decompose NO _x gas adsorbed by the titanium oxide.

In addition, the NO _x gas adsorption / decomposition agent produced by the production method of the present embodiment has a uniform porous material particle (primary particle) of 10 to 15 nm and a small average particle diameter. Moreover, this primary particle has a 0.1-1 nm micropore. Moreover, the porosity of the porous material is about 60%. In addition, by further proceeding the condensation polymerization reaction, primary fine particles are bonded to each other, and a porous material particle (secondary particle) having a three-dimensional structure with many gaps can be formed. Moreover, it can also be set as the form of a porous film as needed.

[3] NO _x gas adsorption decomposition method When the NO _x gas adsorption decomposition agent according to the present invention is brought into contact with NO _x gas, the NO _x gas is adsorbed by the NO _x gas adsorption decomposition agent and decomposed. The temperature for carrying out the NO _x gas adsorption decomposition method is preferably 0 to 300 ° C.

Further, the NO _x gas adsorption / decomposition agent can be used in a powder state. In this case, a powdered NO _x gas adsorption / decomposition agent is filled in the reaction tube, and a gas containing NO _x gas is allowed to pass through. Practically, the NO _x gas adsorption / decomposition agent is formed into a three-dimensional structure such as a plate or honeycomb, or is applied to the surface of a substrate such as various fiber materials, metal materials, plastic materials, and wood by the above-described method. It is preferable to make it adhere and arrange | position in a reactor.

The present invention is intended for adsorption / decomposition of NO _x gas, but sulfur oxide, acetic acid gas, hydrogen fluoride gas, and the like known as other acid gases can also be adsorbed / decomposed.

  The invention is illustrated in more detail by the following examples, but should not be limited thereto.

Example 1: According to the present invention NO _x gas adsorption decomposer]
In this example, ethyl silicate (ethyl silicate 40, manufactured by Colcoat Co.) was used as the inorganic alkoxide, ethanol was used as the solvent for the hydrolysis, and a mixed solution thereof was used as a starting material. And water and hydrochloric acid which is the said acid catalyst were added to this mixed solution, and it was set as the hydrolysis liquid (pH 3-6).

  Hydrolysis is performed at 50 ° C. for 60 minutes, and then calcium carbonate is used as the alkaline earth metal carbonate, which is mixed with ethanol as a suspended suspension and mixed uniformly. To obtain a wet gel body. The wet gel body was pulverized and then dried to produce a dry gel body.

  Each above-mentioned composition was mixed in the ratio of the following Table 1.

  Next, tetraisopropyl titanate (manufactured by Kishida Chemical Co., Ltd.) was used as a photocatalyst precursor solution, and the produced dried gel body was impregnated. Each of the above-described compositions was used at the ratio shown in Table 1 below.

  After impregnation, drying was performed at 120 ° C. for 3 hours, followed by baking at 700 ° C. for 4 hours.

As a result, an NO _x gas adsorption / decomposition agent (particulate) according to the present invention in which the surface of calcium oxide scattered on silica gel was coated with anatase-type titanium oxide was obtained.

[Comparative Example 1]
When verifying the adsorptive decomposition performance of the NO _x gas adsorbing and decomposing agent produced by the above procedure for NO _x gas, a comparative oxidizing gas adsorbing and decomposing performance not impregnated with tetraisopropyl titanate was produced. Each composition of the comparative oxidizing gas adsorption decomposition performance is as shown in Table 1 described above. The gelled wet gel body is pulverized and then dried to form a particulate dry gel body.

[Evaluation of decomposition performance for NO _x gas]
After 1 g of the NO _x gas adsorption / decomposition agent powder obtained in Example 1 and Comparative Example 1 was put in a 500 mL glass container and sealed, nitrogen monoxide gas (NO _x gas) was put in each glass container. The concentration of nitric oxide in the air in the glass container was 100 ppm. And after irradiating with ultraviolet rays using a handy UV lamp (SLUV-8, manufactured by ASONE) for 15 minutes at room temperature (25 ° C.), using a gas detector tube (manufactured by Gastec Co., Ltd.), glass The nitrogen oxide concentration in the container was measured.

As a result, the nitrogen oxide concentration in the glass container containing the NO _x gas adsorption / decomposition agent according to the present invention obtained in Example 1 was 1 ppm. That is, it was found that 99% of the nitrogen oxides were adsorbed and decomposed.

In contrast, the nitrogen oxide concentration in the glass container containing the comparative NO _x gas adsorption decomposing agent obtained in Comparative Example 1 was 15 ppm. That is, it was found that 85% of the nitrogen oxides were adsorbed and decomposed.

In addition, when the glass container containing the NO _x gas adsorption / decomposition agent obtained in Example 1 was left at room temperature (25 ° C.) for 15 minutes without being irradiated with ultraviolet rays, the nitrogen oxide concentration in the glass container was It was 4 ppm. That is, it was found that 96% of the nitrogen oxides were adsorbed and decomposed.

From the above results, the presence of the photocatalyst on the surface of the alkaline earth metal oxide dispersed in the porous material, as in the present invention, makes it possible to efficiently adsorb NO _x gas compared to the conventional case. It was shown that degradation can be performed. This is considered to be largely due to the photocatalyst present on the surface of the oxide of the alkaline earth metal from the difference in the measurement results depending on the presence or absence of ultraviolet irradiation.

It can be said that the present invention is characterized by the following configuration. That is, the NO _x gas adsorption / decomposition agent according to the present invention is a polycondensation of a silica sol obtained by hydrolyzing a silicon alkoxide solution by a sol-gel method in the presence of an alkaline earth metal carbonate and / or hydroxide. In other words, it can be said that the obtained silica gel is impregnated with a titanium oxide precursor compound solution and heated and fired. In the above structure, the alkoxide of silicon is preferably ethyl silicate. In the above structure, the alkaline earth metal is preferably magnesium and / or calcium. Furthermore, in the above configuration, the titanium oxide precursor compound is preferably tetraisopropyl titanate. Furthermore, the method for producing an NO _x gas adsorption / decomposition agent according to the present invention comprises a silica sol obtained by hydrolyzing a silicon alkoxide solution by a sol-gel method, in the presence of an alkaline earth metal carbonate and / or hydroxide. In other words, it can be said that the silica gel obtained by polycondensation is impregnated with a titanium oxide precursor compound solution and heated and fired.

According to the acid gas adsorption / decomposition agent and the method for producing the same according to the present invention, it is possible to provide an acid gas adsorption / decomposition agent that efficiently adsorbs and decomposes NO _x gas contained in the atmosphere or the like.

Therefore, such a NO _x gas adsorption decomposer, air cleaner, an outdoor (for example, roads and tunnels) can be suitably used for an exhaust gas purifying device or the like in.

Claims (12)

An NO _x gas adsorption / decomposition agent, characterized in that an alkaline earth metal oxide is dispersed in a porous material, and a photocatalyst is attached to at least a part of the surface of the oxide. The NO _x gas adsorption / decomposition agent according to claim 1, wherein the porous material is silica gel. The NO _x gas adsorption / decomposition agent according to claim 1 or 2, wherein the photocatalyst is titanium oxide. The NO _x gas adsorption / decomposition agent according to any one of claims 1 to 3, wherein the alkaline earth metal is magnesium or calcium. A photocatalyst precursor solution is obtained by polycondensing a sol obtained by hydrolyzing an inorganic alkoxide solution by a sol-gel method in the presence of an alkaline earth metal carbonate and / or hydroxide. A method for producing an NO _x gas adsorption / decomposition agent, characterized by impregnating with heat and baking. The method for producing an NO _x gas adsorption / decomposition agent according to claim 5, wherein the gel body impregnated with the photocatalyst precursor solution has a particle shape. The method for producing an NO _x gas adsorption / decomposition agent according to claim 5 or 6, wherein a silicon alkoxide is used as the inorganic alkoxide. The method for producing an NO _x gas adsorption / decomposition agent according to any one of claims 5 to 7, wherein tetraethoxysilane is used as the silicon alkoxide. The method for producing an NO _x gas adsorption / decomposition agent according to any one of claims 5 to 8, wherein magnesium or calcium is used as the alkaline earth metal. The method for producing an NO _x gas adsorption / decomposition agent according to any one of claims 5 to 9, wherein tetraisopropyl titanate is used as the photocatalyst precursor solution. NO _x gas adsorption decomposer manufactured by the manufacturing method according to any one of claims 5 to 10. NO _x gas adsorption decomposing agent according to any one of claims 1 to 4, or the NO _x gas adsorption decomposing agent according to claim 11, by contacting the NO _x gas, the NO _x gas adsorption decomposition A NO _x gas adsorption decomposition method comprising adsorbing NO _x gas to an agent and decomposing the NO _x gas by the photocatalyst.