JPH07213900A - Catalyst for decomposition and removal of nitrogen oxide and its production - Google Patents

Abstract

PURPOSE:To obtain a catalyst excellent in strength and dimensional accuracy and having excellent activity for decomposition and removal of nitrogen oxides by burning a molded body containing praseodymium oxide and a molding assistant. CONSTITUTION:This catalyst consists of a molded body containing praseodymium oxide and a molding assistant or a burnt body obtd. by burning this molded body. The molding assistant is one or more kinds selected from among beta-1,3- glucan, clay minerals, inorg. fibers, cellulose compds., polyvalent hydroxy compds., and polyvinyl polymers. With this catalyst, nitrogen oxides are decomposed and removed without the presence of a reducing agent or in the presence of O2 by bringing the catalyst into contact with nitrogen oxides. The praseodymium oxide compsn. for molding has excellent plastic molding property, and for example, it can be formed in a desired shape by extrusion molding. The molded body is dried, and if necessary, burnt. Thus, the praseodymium oxide molded body or praseodymium oxide molded and burnt body excellent in strength and dimensional accuracy can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for removing harmful nitrogen oxides in various exhaust gases. Specifically, the present invention is a praseodymium oxide-containing molded product and molded fired product useful as a catalyst for decomposition and removal of nitrogen oxides,
The present invention relates to a production method, a production intermediate and a method for decomposing and removing nitrogen oxides using the catalyst.

[0002]

2. Description of the Related Art Removal of air pollutants emitted when various fuels are burned is an important social issue from the viewpoint of environmental protection. In particular, nitrogen oxides (hereinafter also referred to as NOx) contained in combustion exhaust gas emitted from fixed sources such as factories and mobile sources such as automobiles are considered to be the cause of photochemical smog and acid rain. Its removal is an urgent task at present.

Conventionally, it has been known that a metal oxide is effective as a catalyst for directly decomposing and removing nitrogen oxide (Plenum Press, New York (1975), p63). For example,
It has been reported that a catalyst containing an oxide of a metal element such as manganese, cobalt, chromium, or copper can be used for catalytic thermal decomposition of NO ₂ (Japanese Patent Publication No. 3-56779). Also,
For the purpose of improving the decomposition activity of nitrogen oxides of metal oxides, on a carrier such as zeolite, iron, vanadium, molybdenum, tungsten, nickel, cobalt,
A catalyst supporting an oxide of a metal such as copper, chromium or uranium has been proposed (Japanese Patent Publication No. 60-12909).
Tokushuhei 2-500822). Furthermore, a method of removing nitrogen oxides in exhaust gas by contacting a catalyst containing a metal oxide or a catalyst in which a metal oxide is supported on a carrier with nitrogen oxides in the presence of ammonia has been proposed ( JP-A-50-75969, JP-A-59-513
39, JP-A-63-294950). Further, a method for decomposing nitrogen oxides using a catalyst in which silver is contained in a metal oxide as a co-catalyst metal has been proposed (JP-A 1-2).
24047). However, in these documents, there is no mention of a catalyst for decomposition and removal of nitrogen oxides containing praseodymium oxide.

On the other hand, as a catalyst for decomposing and removing nitrogen oxides containing praseodymium oxide, nitrogen oxidation composed of a composite metal oxide composed of one or more elements selected from praseodymium and the like, strontium and nickel. A substance reduction catalyst has been proposed, but this catalyst requires a reducing agent such as carbon monoxide or hydrocarbon in order to reduce nitrogen oxides to nitrogen (Japanese Patent Laid-Open No. 48-9228).
9 gazette). Also, in the alumina hydrate, at least one rare earth element oxide selected from praseodymium,
And copper oxide, and in some cases after mixing a powder of a mixed or complex oxide consisting of zirconium oxide is molded, then a method for producing a catalyst characterized by calcining this molded body, is proposed, In order for the catalyst obtained by this production method to decompose and remove nitrogen oxides into harmless gases such as nitrogen, a reducing gas such as ammonia or carbon monoxide is required (Japanese Patent Laid-Open No. 50-24181). Thus, the present situation is that no catalyst has been proposed that decomposes and removes nitrogen oxides containing praseodymium oxide and that does not require any reducing agent to decompose and remove nitrogen oxides.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a molded product containing praseodymium oxide, which is useful as a catalyst for decomposing and removing nitrogen oxides, a molded fired product, and a molding composition having improved plastic moldability which is an intermediate for the production thereof. It is an object of the present invention to provide a product, a molding composition, a molded product, a method for producing a molded and baked product, and a method for decomposing and removing nitrogen oxides using the catalyst.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that among various metal oxides, praseodymium oxide is particularly excellent regardless of the presence or absence of a reducing agent. It has been found that it has the activity of directly decomposing and removing nitrogen oxides. Further, they have found that a molding composition having excellent moldability can be obtained by adding a molding aid such as β-1,3-glucan to the praseodymium oxide. Further, by molding this molding composition, and further firing, without unexpectedly lowering the function as a catalyst carrier, to ensure industrially practical mechanical strength, without cracking, strength and It has been found that a molded product and a molded fired product having excellent dimensional accuracy can be easily obtained. It was also found that these molded products and molded fired products also exhibit extremely excellent ability to decompose and remove nitrogen oxides regardless of the presence or absence of a reducing agent. The present inventors have completed the present invention as a result of further research based on these findings.

That is, the present invention provides (1) a catalyst for decomposing and removing nitrogen oxides, characterized by containing praseodymium oxide alone as a catalyst component, (2) praseodymium oxide and β-1,3-glucan, and clay A molded product containing one or more molding aids selected from the group consisting of minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds and polyvinyl polymers, or a baked product. A catalyst for decomposing and removing nitrogen oxides, which is a molded and fired product obtained by the above, and (3) a nitrogen oxide according to item (1) or (2), which is a honeycomb structure. Decomposition removal catalyst, (4) Nitrogen oxide decomposition removal catalyst according to (1) to (3), which directly decomposes and removes nitrogen oxides in the absence of a reducing agent.
(5) praseodymium oxide and one or more molding aids selected from the group consisting of β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. A molding composition comprising (6) praseodymium oxide and β-
Molding containing one or two or more molding aids selected from the group consisting of 1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. And (7) a honeycomb structure, which is obtained by firing the molded product of (6) or (8) (6) or (7). And (9) a method for decomposing and removing nitrogen oxide, characterized in that the catalyst for decomposing and removing nitrogen oxide according to (1) to (3) is brought into contact with nitrogen oxide, The method for decomposing and removing nitrogen oxides according to item (9), which is carried out in the absence of a reducing agent. (11) The method (9) or (10), which is carried out in the presence of O _2. Method for decomposing and removing nitrogen oxides according to item (12) Acid Mixing praseodymium with one or more molding aids selected from the group consisting of β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. (5) A method for producing a molding composition according to (5), (13) A molding composition according to (5) is extrusion-molded, wherein (6) or (7) is present. A method for producing a molded article, (14) A method for producing a molded and fired article according to item (8), which comprises firing the molded article according to item (6) or (7).

More specifically, the present invention is (15) a molded product characterized by containing praseodymium oxide alone as a catalyst component or a molded and baked product obtained by baking the molded product. And a catalyst for decomposing and removing nitrogen oxides according to item (1), further comprising (16) cobalt, manganese, chromium, iron, vanadium, molybdenum, tungsten, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium. A catalyst for decomposing and removing nitrogen oxides according to any one of (1) to (3), which contains an oxide of one or more metal elements selected from the group:
(17) The catalyst for decomposing and removing nitrogen oxides according to the item (16), wherein the metal element is cobalt and / or thallium.
(18) β- with respect to 100 parts by weight of praseodymium oxide
Contains 0.1 to 300 parts by weight of one or more molding aids selected from the group consisting of 1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. The catalyst for decomposing / removing nitrogen oxides according to the item (2), characterized in that (19) the molding aid is β-1,3-glucan and / or a clay mineral (2) or (18) The catalyst for decomposing / removing nitrogen oxides according to item (20), containing 0.1 to 20 parts by weight of β-1,3-glucan and 5 to 50 parts by weight of clay mineral per 100 parts by weight of praseodymium oxide. A catalyst for decomposing and removing nitrogen oxides according to the item (19),

(21) Further, cobalt, manganese, chromium, copper, iron, vanadium, molybdenum, tungsten,
Decomposition of nitrogen oxides according to item (2), which contains an oxide of one or more metal elements selected from the group consisting of strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium. Removal catalyst, (22) Nitrogen oxide decomposition removal catalyst according to item (21), wherein the metal elements are cobalt and / or thallium, (23) Cobalt, manganese, chromium with respect to 100 parts by weight of praseodymium oxide. Oxide of one or more metal elements selected from the group consisting of copper, iron, vanadium, molybdenum, tungsten, strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium 0.01
1 to 10,000 parts by weight (2
(1) A catalyst for decomposing and removing nitrogen oxides, (24) The praseodymium oxide is Pr ₆ O ₁₁ (1) to (4),
(17) to (23), the catalyst for decomposing nitrogen oxides, (25) β-1,3-glucan is curdlan, (2), (18) to (20), (26) A catalyst for decomposing / removing a substance, wherein the clay mineral is a 1: 1 layer type clay mineral and / or a 2: 1 layer type clay mineral (2),
The catalyst for decomposing and removing nitrogen oxides according to (18) to (20), (27) the weight ratio of the 1: 1 layer type clay mineral to the 2: 1 layer type clay mineral is 10:90 to 95: 5. The catalyst for decomposing and removing nitrogen oxides according to (26), (28) β-1,3-glucan, relative to 100 parts by weight of praseodymium oxide,
Characterized by containing 0.1 to 300 parts by weight of one or more molding aids selected from the group consisting of clay minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds and polyvinyl polymers. (5) The molding composition according to (5), (29) The molding aid is β-1,3-glucan and / or a clay mineral (5) or (28)
(30) Praseodymium oxide 10 (10)
Β-1,3-glucan 0.1 to 20 parts by weight relative to 0 parts by weight
The composition for molding according to item (29), characterized by containing 5 parts by weight and 5 to 50 parts by weight of a clay mineral,

(31) Further, cobalt, manganese, chromium, copper, iron, vanadium, molybdenum, tungsten,
The molding composition according to item (6), which contains an oxide of one or more metal elements selected from the group consisting of strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium,
(32) The molding composition according to item (31), wherein the metal element is cobalt and / or thallium, (33) cobalt, manganese, chromium, copper, iron, vanadium, relative to 100 parts by weight of praseodymium oxide. Contain 0.01 to 10,000 parts by weight of an oxide of one or more metal elements selected from the group consisting of molybdenum, tungsten, strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium. The molding composition according to item (31), (34) the molding composition according to items (5) and (28) to (33), wherein praseodymium oxide is Pr ₆ O ₁₁ ,
(35) The molding composition according to (5) or (28) to (30), wherein the β-1,3-glucan is curdlan.
(36) The clay mineral is a 1: 1 layer type clay mineral and / or a 2: 1 layer type clay mineral (5), (28) to
(30) The molding composition according to the item (37), wherein the weight ratio of the 1: 1 layer type clay mineral to the 2: 1 layer type clay mineral is 10:90 to.
The molding composition according to item (36), which is 95: 5, (3
8) With respect to 100 parts by weight of praseodymium oxide, β-1,
0.1 to 300 parts by weight of one or more molding aids selected from the group consisting of 3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. (6) The molding according to (6), wherein the molding aid is β-1,3.
-Glucan and / or clay mineral, the molded article according to item (6) or (38), and (40) praseodymium oxide 100 parts by weight, and β-1,3-glucan 0.1.
To 20 parts by weight and 5 to 50 parts by weight of clay mineral, the molded product according to item (39), (41)
Furthermore, one or more metal elements selected from the group consisting of cobalt, manganese, chromium, copper, iron, vanadium, molybdenum, tungsten, strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium. The molded product according to item (6), which contains an oxide, (42) the molded product according to item (41), wherein the metal element is cobalt and / or thallium.

(43) Containing 100 parts by weight of praseodymium oxide, cobalt, manganese, chromium, copper, iron, vanadium, molybdenum, tungsten, strontium, nickel, chromium, uranium, thallium, lanthanum, cerium, neodymium and samarium. Oxide of one or more metal elements selected from the group 0.01
1 to 10,000 parts by weight (4)
The molded article according to item 1), wherein (44) praseodymium oxide is Pr.
The (6) ₆ O _11, (38) - (43) molded product according to claim, (45) a beta-1,3-glucan is curdlan (6), (38) - (40) A molded article according to item (4
6) The clay mineral is a 1: 1 layer type clay mineral and / or
2: 1 layer type clay minerals (6), (38) to (4)
The molded product according to item 0), wherein the weight ratio of (47) 1: 1 layer type clay mineral to 2: 1 layer type clay mineral is 10:90 to 95: 5.
(48) No. (38)
A molded fired product obtained by firing the molded product according to (47), and (49) the nitrogen oxide is NO (1) to
(4) The catalyst for decomposition and removal of nitrogen oxides according to (15) to (27) and the catalyst for decomposition and removal of nitrogen oxides according to (50) (15) to (27) are brought into contact with nitrogen oxides. (51) A method for decomposing and removing nitrogen oxides, (51) A method for decomposing and removing nitrogen oxides, which comprises: (51) a method for decomposing and removing nitrogen oxides; and (52) in the presence of O ₂ . The method for decomposing and removing nitrogen oxides according to item (50) or (51), which is characterized in that (53) about 200 to 7
No. (9) to (1) characterized by being performed at a temperature of 00 ° C.
1), the method for decomposing and removing nitrogen oxides according to (50) to (52), and (54) the description of (9) to (11) and (50) to (53), wherein the nitrogen oxide is NO. And a method for decomposing and removing nitrogen oxides.

The catalyst for decomposing and removing nitrogen oxides of the present invention is
(1) What is characterized by containing praseodymium oxide alone as a catalyst component, preferably what is characterized by being a molded product containing praseodymium oxide alone as a catalyst component, or by firing the molded product. Or a (2) praseodymium oxide and β-1,3-glucan, clay mineral, inorganic fiber, cellulosic compound, polyvalent hydroxy compound, polyvinyl polymer, etc. What is characterized by being a molded product containing one or more molding aids selected from the group consisting of, or a molded fired product obtained by baking the molded product. Is. As praseodymium oxide used in the catalyst of the present invention, for example, Pr ₆ O ₁₁ , Pr ₂ O ₃ , PrO ₂ or a mixture thereof is used. Of these, Pr ₆ O _{11 and the} like are preferable. These praseodymium oxides may be commercially available products, or may be those obtained by synthesis or those obtained by firing. As commercially available praseodymium oxide,
For example, Pr ₆ O ₁₁ ("praseodymium oxide" 96% or more,
Nikki) is used. As those obtained by synthesis, for example, water-soluble praseodymium salt (praseodymium chloride, praseodymium bromide, praseodymium iodide, praseodymium sulfate, praseodymium nitrate, cobalt oxide synthesized by a method known per se using praseodymium acetate, etc.) Examples of the product obtained by firing include water-soluble praseodymium salts (praseodymium chloride, praseodymium bromide, praseodymium iodide, praseodymium sulfate,
Cobalt oxide, praseodymium hydroxide or praseodymium carbonate, which is synthesized by a method known per se using praseodymium nitrate, praseodymium acetate, etc.
00 ° C, preferably 400 to 700 ° C, usually 0.5 to
A calcined product obtained by calcining for 24 hours, preferably 1 to 5 hours is used. More preferable firing conditions include an oxidizing atmosphere and the like, and the firing rate and the like should be appropriately selected.

In the present invention, a nitrogen oxide decomposition and removal catalyst characterized by containing praseodymium oxide alone as a catalyst component contains one or more of the above praseodymium oxides. The catalyst, other than praseodymium oxide as a catalyst component, cobalt, manganese, chromium, iron, vanadium, molybdenum, tungsten, chromium, uranium, thallium, lanthanum, cerium,
One or more oxides of metal elements such as neodymium and samarium can be contained. Among these metal oxides, particularly, it is preferable to contain an oxide of a metal element such as cobalt, thallium, lanthanum, cerium, neodymium, or samarium, more preferably, an oxide of a metal element such as cobalt or thallium. . Examples of the cobalt oxide include CoO, Co ₂ O ₃ and Co.
₃ O ₄ or a mixture thereof is used. These cobalt oxides are commercially available (for example, Wako Pure Chemicals Reagent etc.)
Or may be obtained by firing. Among cobalt oxides, Co ₃ O ₄ is preferable.
This Co ₃ O ₄ may be a commercially available product (for example, Wako Pure Chemicals Reagent, etc.), or may be C by firing.
A water-insoluble cobalt compound that changes to o ₃ O ₄ is usually added to 300
To 800 ° C., preferably 400 to 700 ° C., usually 0.
It may be a fired product obtained by firing for 5 to 24 hours, preferably about 1 to 5 hours. More preferable firing conditions include an oxidizing atmosphere and the like, and the firing rate and the like should be appropriately selected. The main component of this fired product is Co ₃ O ₄
Is. Examples of the water-insoluble cobalt compound that changes into Co ₃ O ₄ by firing include cobalt oxide (eg, CoO, Co ₂ O ₃ , Co ₃ O ₄ ) or its hydrate (eg, cobalt hydroxide), carbonic acid. One or more selected from cobalt or its hydrate, basic cobalt carbonate or its hydrate, cobalt oxalate and the like are used. Among them, cobalt hydroxide, cobalt carbonate, basic cobalt carbonate, cobalt oxalate, Co
O, Co ₂ O ₃ , Co ₃ O ₄ or a mixture thereof is preferable. These water-insoluble cobalt compounds are commercially available, for example, basic cobalt carbonate (eg, special cobalt carbonate, manufactured by Nippon Kagaku Sangyo or Wako Pure Chemicals Reagent), Co ₂ O ₃
(Co ₂ O ₃ , Wako Pure Chemicals Reagent, 99.5%), Co ₃ O
₄ (Co ₃ O ₄ , for Wako Pure Chemical), cobalt oxide (cobalt oxide, manufactured by Nippon Kagaku Sangyo Co., Ltd.) and the like are used, and further, water-insoluble cobalt salts (eg, cobalt sulfate, cobalt acetate, cobalt chloride, fluorine). Cobalt hydroxide, basic cobalt carbonate, cobalt carbonate, etc. obtained by synthesizing by a method known per se using (cobalt oxide, cobalt nitrate, etc.) can also be used. As the oxide of thallium, Tl ₂ O, Tl ₂ O ₃ or a mixture thereof is used. Of these, Tl ₂ O ₃ is preferable. Thallium oxide may be commercially available, may be obtained by synthesis, or may be obtained by firing. Examples of commercially available thallium oxide include thallium oxide (Tl ₂
O ₃ , manufactured by Wako Pure Chemical Industries, Ltd., etc. are used. As the compound obtained by synthesis, for example, a water-soluble thallium salt (thallium fluoride, praseodymium chloride, thallium perchlorate, thallium triiodide, thallium hydroxide, thallium carbonate, praseodymium acetate, etc. can be used by a method known per se. The thallium oxide synthesized in 1. is used, and the one obtained by firing is, for example, a water-soluble thallium salt (thallium fluoride,
Thallium chloride, thallium perchlorate, thallium triiodide,
Thallium oxide synthesized by a method known per se using thallium hydroxide, thallium carbonate, thallium acetate, etc. is usually 300 to 800 ° C., preferably 400 to 700 ° C., usually 0.5 to 24 hours, preferably 1 to Those obtained by firing for about 5 hours are used.

The above-mentioned metal oxides other than praseodymium oxide are usually contained in an amount of about 0.
01 to 10000 parts by weight, preferably about 1 to 10000
It is suitable to add about 10 parts by weight, more preferably about 10 to about 200 parts by weight. In particular, oxides of metal elements such as lanthanum, cerium, neodymium, and samarium are usually used in an amount of about 0.01 to 10 with respect to 100 parts by weight of praseodymium oxide.
It is suitable to add about 1 to 5 parts by weight, preferably about 0.01 to 5 parts by weight. It is suitable to add about 1 to 10000 parts by weight, preferably about 5 to 500 parts by weight, of oxides of metal elements such as cobalt and thallium to 100 parts by weight of praseodymium oxide. The catalyst for decomposition and removal of nitrogen oxides, which contains praseodymium oxide alone as the catalyst component of the present invention or further contains the above metal oxide, may contain any molding aid, catalyst carrier or the like as described below. Good. In the case of producing a catalyst for decomposition and removal of nitrogen oxides containing praseodymium oxide alone as the catalyst component of the present invention, praseodymium oxide, if necessary, other metal oxides, a molding aid and / or a catalyst carrier are used as raw materials. It can be molded into an arbitrary shape according to a method known per se, and can be further baked. For example, granules,
It can be used as a spherical material, a round bar, a square bar, a hollow tube, a thin plate, a sheet, a film, a honeycomb structure and the like. For example, granules can be produced by pellet molding equipment (SE Work Press WPM
-10 type and SE soybean, manufactured by Toyo Hydraulic Machinery Co., Ltd. The honeycomb structure can be formed by an extrusion molding method of cobalt oxide (for example, an extruder, a DE-35 type manufactured by Honda Iron Works Co., Ltd.). The molded fired product is. These molded products are about 115
It can be manufactured by drying at ℃ and baking at about 300 to 800 ℃. For example, in the case of granules and spheres,
The particle size is not limited as long as it is a practical size, but the particle size is usually 0.5 to 50 mm, preferably 1 to 20 mm. Further, in the case of a honeycomb structure, it is preferable that the aperture ratio is large. This is because when liquid or gas comes into contact with the zeolite and flows, it can pass without receiving resistance (that is, low pressure loss). The aperture ratio is usually 50 to 90%, preferably 50 to 80%, and more preferably 55 to 80%. The number of cells is usually 10 to 600 cells / square inch, preferably 20 to 40
The range is 0 cells / square inch. Furthermore, praseodymium oxide of the present invention is a plate such as metal or ceramic, sphere,
It can also be used in a form coated with a wash coat on the surface of a honeycomb substrate or the like. The amount of praseodymium oxide used varies depending on the place of use, scale of use, etc., and can be appropriately selected according to the purpose.

Further, in producing the catalyst having the above-mentioned shape, the above-mentioned water-soluble praseodymium salts (praseodymium chloride, praseodymium bromide, praseodymium iodide, praseodymium sulfate, praseodymium nitrate, praseodymium acetate, etc. are known per se. Cobalt oxide, praseodymium hydroxide or praseodymium carbonate synthesized by the above method, and other metal oxides described above as necessary, or a raw material compound which is converted to the above metal oxide by firing, a molding aid and / or After molding the catalyst carrier into a desired shape, it is usually 300 to 800 ° C., preferably 400 to 70.
The catalyst of the present invention can also be produced by calcining at 0 ° C for usually 0.5 to 24 hours, preferably 1 to 5 hours. The catalyst of the present invention is preferably one or two selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds, polyvinyl polymers and the like.
It is characterized by being a molded product containing one or more molding aids, or a molded and baked product obtained by baking the molded product. Hereinafter, a molding composition containing a praseodymium oxide of the present invention, a molded article, a detailed description of the molded fired product, a molded article containing the praseodymium oxide of the present invention and the molding aid,
A catalyst for decomposition and removal of nitrogen oxides, which is a molded and fired product obtained by firing the molded product, will be described. The molding composition of the present invention is one or two selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds, polyvinyl polymers and the like. It contains the above molding aid.

The molding composition of the present invention may contain other metal oxides in addition to praseodymium oxide. For example,
Cobalt, manganese, chromium, copper, iron, vanadium, molybdenum, tungsten, strontium, nickel,
One or more oxides of metal elements such as chrominium, uranium, thallium, lanthanum, cerium, neodymium, and samarium can be contained. Among these metal oxides, it is particularly preferable to contain an oxide of a metal element such as cobalt, thallium, lanthanum, cerium, neodymium, or samarium, preferably an oxide of a metal element such as cobalt or thallium. As the cobalt oxide and the thallium oxide, the same ones as described above are used. The above metal oxide other than praseodymium oxide is usually about 0.01 to 10000 parts by weight, preferably about 1 to 10000 parts by weight, and more preferably 10 to 2 parts by weight based on 100 parts by weight of praseodymium oxide.
It is preferable to add about 00 parts by weight. In particular, the oxide of a metal element such as lanthanum, cerium, neodymium, or samarium is usually about 0.01 to 10 parts by weight, preferably about 0.01 to about 100 parts by weight of praseodymium oxide.
It is preferable to add about 5 parts by weight. Oxides of metal elements such as cobalt and thallium are praseodymium oxide 10
It is suitable to add about 10 to 10,000 parts by weight, preferably about 5 to 500 parts by weight, relative to 0 parts by weight. In the molding composition of the present invention, one or more moldings selected from the group consisting of β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds, polyvinyl polymers and the like. The auxiliary agent is usually about 0.1 to 300 per 100 parts by weight of praseodymium oxide.
Parts by weight, preferably about 0.1 to 150 parts by weight.

Β-used in the composition of the present invention
1,3-Glucan mainly acts as a plasticizer for praseodymium oxide. This β-1,3-glucan is a glucan in which glucose is mainly bound by β-1,3-bonds, and specifically, curdlan,
Laminaran, baramilon, callose, pakiman and the like are used. Among these β-1,3-glucans, β-1,3-glucan of microbial origin is preferable, and therefore curdlan, paramylon and the like are preferably used, and curdlan is most preferably used. All of these give high plasticity to praseodymium oxide when used in small amounts. Curdlan is New Food Industry, No. 20
As described in Volume No. 10, pp. 49-57 (1978), mainly composed of β-1,3-glucoside bonds,
Polysaccharides that have heat coagulability, that is, they coagulate (form a gel) when heated in the presence of water.
It is a β-1,3-glucan having properties. Such curdlan is produced by microorganisms of the genera Alcaligenes or Agrobacterium or thallium oxide. Specific examples of such microorganisms include, for example, Alcaligenes faecalis barr Myxogenes strain 10C.
3K (Agricultural Biological Chemistry, No. 30
Vol. 196 (1966)), or Alcaligenes fuecalis bar Myxogenes strain 10C3K.
Mutant of NTK-u (IFO 13140) (Japanese Patent Publication No. 48)
-32673), Agrobacterium or thallium oxide radiobacterium (IFO 13127) and its mutant U-19 (IFO 12126) (Japanese Patent Publication No. 48-
32674) and the like can be used. Curdlan is a β-produced by microorganisms as described above.
Although a kind of 1,3-glucan, in the present invention,
This may be used as it is, or may be highly purified before use.

Paramylon is a type of β-1,3-glucan that is accumulated in cells by the microorganism Euglena. Paramylon is, for example, Carbohydrate R
It is already known from esearch, 25 , 231-242 (1979), JP-A-1-37297, and the like.
In addition, paramylon may be alkali-treated, if necessary, in order to have heat-coagulability. In the present invention, paramylon may be used as it is in an unpurified form, or may be highly purified before use, if necessary. Similarly, other β-1,3-glucans may be used in an unpurified state, or may be highly purified before use, if necessary. In particular, β-1,3-
Among the glucans, curdlan having a heat-coagulability and paramylon treated with an alkali are most preferably used. By using β-1,3-glucan having such heat coagulability as a plasticizer, a kneading solid composition having sufficient moldability in the process of molding, drying and firing praseodymium oxide or thallium oxide, Thus, a molded product having sufficient strength can be obtained. As described above, β-1,3-glucan is necessary for imparting molding plasticity to praseodymium oxide, which originally has no molding plasticity. In the molding composition of the present invention, a clay mineral can be used in order to improve the moldability and further maintain the strength of the fired product after firing. As the clay mineral, 1: 1 layer type clay mineral, 2: 1 layer type clay mineral and the like are used. As a 1: 1 layer type clay mineral,
For example, a kaolinite group mineral is used. In particular,
Examples include kaolinite, halloysite, datesite, lizardite, amethite, natural clay (kibushi clay, frog eye clay, etc.). These may be used alone or in combination of two or more. Of these, kaolinite, halloysite, kibushi clay and the like are preferably used. On the other hand, examples of the 2: 1 layer type clay mineral include, for example, pyrophyllite group minerals (pyrophyllite, etc.),
Smectite group minerals (montmorillonite, bentonite, synthetic smectite, hectorite, etc.) and vermiculite group minerals (vermiculite, etc.) are used. Preferably, a smectite group mineral is used. Among them, bentonite and synthetic smectite are particularly preferable. These clay minerals can be used alone,
It is more preferable to use the 1: 1 layer type clay mineral and the 2: 1 layer type clay mineral together for the following reasons. The 1: 1 layer type clay mineral is a sintering agent that has the effect of increasing the mechanical strength of the praseodymium oxide molded fired product described below. However, during extrusion molding, the mineral molecules are oriented in layers, and interlayer slippage easily occurs. Therefore, when the 1: 1 layer type clay mineral is used alone or when the weight ratio is large, cracks are likely to occur in the layer direction in which the molecules are oriented, and cracks are likely to occur. As a result, the mechanical strength of the molded product of praseodymium oxide is not satisfactory. On the other hand, the 2: 1 layer type clay mineral
Since it is finely crystalline, it is difficult to orient in a layered form. Therefore, if this is mixed with an appropriate amount of 1: 1 layer type clay mineral, the above 1:
It is possible to compensate for the drawbacks of the one-layer type clay mineral. Further, when the 2: 1 layer type clay mineral is used alone or when the weight ratio thereof is large, the moldability of the kneaded solid composition for praseodymium oxide molding is poor and it becomes difficult to apply it to extrusion molding. A molded product obtained by extrusion-molding such a composition does not have a smooth molded surface and is inferior in strength.

In the molding composition of the present invention, inorganic fibers can be blended as a reinforcing material. Examples of the inorganic fiber include glass fiber, carbon fiber, alumina fiber, silica fiber, alumina silicate fiber, rock wool, zirconia fiber, silicon carbide fiber, titanium fiber, boron fiber, magnesia fiber, slag wool, asbestos. , Sepiolite and the like. Among these, glass fiber and sepiolite are preferably used. In the molding composition of the present invention, in order to impart higher plastic moldability to praseodymium oxide, usual auxiliary agents for molding other than those described above can be used. As the auxiliary agent,
For example, cellulosic compounds, polyhydroxy compounds,
Alternatively, a polyvinyl polymer or the like is preferably used. Examples of the cellulose-based compound include methyl cellulose,
Ethyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose and the like can be used. As such a cellulosic compound, any commercially available one can be used regardless of its molecular weight and the like, and is appropriately selected according to the application. As the polyhydric hydroxy compound, for example, alkylene glycol such as glycerin, ethylene glycol, propylene glycol, triethylene glycol, and 1,3-butylene glycol, polyoxyalkylene glycol such as polyethylene glycol and polypropylene glycol, and the like can be used. . As for these polyhydric hydroxy compounds, all commercially available compounds can be used regardless of the molecular weight and the like, and are appropriately selected according to the application. Examples of the polyvinyl polymer include polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid resin, and polyacrylic acid salts such as ammonium polyacrylate, acrylic acid-maleic acid copolymer, and ammonium salts thereof. The polyacrylic acid resin may be crosslinked. Such cross-linked polyacrylic acid resin is already known and can be obtained as a commercial product. As for these polyvinyl polymers, any commercially available products can be used regardless of the molecular weight and the like, and they are appropriately selected depending on the application.

In addition to the above, various organic substances can be used as an auxiliary agent. For example, carboxymethyl starch, sodium alginate, ammonium alginate and the like can be used. These auxiliaries may be used alone or as a mixture of two or more kinds. Among the above, for example, methylcellulose-based molding aids such as methylcellulose, hydroxypropylmethylcellulose and hydroxyethylmethylcellulose are preferably used. Especially 2% of these
The viscosity of the aqueous solution at 20 ° C. is preferably 20 to 100,000 centipoise, and more preferably 400 to 100,000 centipoise. Further, in the present invention, if necessary, an alkyl ether of polyethylene glycol, a surfactant known as a wetting agent, a lubricant such as zinc stearate, aluminum stearate, magnesium stearate, etc. are appropriately oxidized for molding. It may be contained in the praseodymium composition or the praseodymium oxide molded product. Among the above molding aids, for example, β-
1,3-glucan, clay minerals and the like are preferable, especially β-
The catalyst containing 1,3-glucan and clay minerals does not crack and becomes a high-strength molded product. In addition, the molding composition of the present invention includes β-1,3-which has a heat-solidifying property.
When glucan, particularly curdlan or alkali-treated paramylon, and a methylcellulose-based molding aid as an auxiliary agent are used together, a molding praseodymium oxide or thallium oxide composition having excellent moldability can be obtained, which will be described later. As described above, after the composition is molded, the heat-coagulable β-1,3-glucan in the molded product is heated and coagulated, and then dried to obtain a molded product having high strength without cracking. . Furthermore, as the polyvalent hydroxy compound, polyethylene glycol, preferably,
By using a resin having a molecular weight of about 6000 and using it in combination with an inorganic fiber, a methylcellulose-based molding aid, etc., a molded product having excellent strength, particularly a molded product having a honeycomb structure can be obtained. In the molding composition of the present invention, β-1,3-glucan, alone or as a mixture of two or more kinds, is usually 0.1 to 20 parts by weight, preferably 0.1 to 100 parts by weight of praseodymium oxide. It is used in the range of 5 to 10 parts by weight.

In the molding composition of the present invention, the clay mineral is usually contained in an amount of 5 to 5 relative to 100 parts by weight of praseodymium oxide.
It is used in an amount of 0 part by weight, preferably 10 to 45 parts by weight. Further, the above-mentioned 1: 1 layer type clay mineral and 2: 1 layer type clay mineral are usually in a weight ratio of 10/90 to 95/5, preferably 30/70 to 90/10, and further preferably Are used in a weight ratio of 55/45 to 85/15. In the molding composition of the present invention, the inorganic fibers are 100 parts by weight of praseodymium oxide,
It is used in the range of 0.1 to 20 parts by weight, preferably 0.2 to 15 parts by weight, and most preferably 0.5 to 10 parts by weight.
In the molding composition of the present invention, a cellulosic compound,
The polyhydric hydroxy compound or polyvinyl polymer is usually about 0.1 (as a total amount when a mixture of two or more kinds is used) per 100 parts by weight of praseodymium oxide.
-30 parts by weight, preferably about 0.2 to 15 parts by weight. Furthermore, in the molding composition of the present invention,
Instead of the above-mentioned molding aid, or in addition to the above-mentioned molding aid, a usual catalyst carrier can be contained. Examples of such a catalyst carrier include aluminum hydroxide, titanium hydroxide, zinc hydroxide, magnesium hydroxide,
Aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, silica, zeolite, etc. are used. In this case, the catalyst carrier is used in the range of 10 to 700 parts by weight, preferably 50 to 600 parts by weight, and most preferably 100 to 500 parts by weight with respect to 100 parts by weight of praseodymium oxide. In the present invention, a molding composition (hereinafter sometimes referred to as a molding praseodymium oxide composition) is produced by mixing praseodymium oxide with the above-mentioned molding aid, and optionally other metal oxides. By molding the molding praseodymium oxide composition by extrusion molding, a molded product (hereinafter, sometimes referred to as praseodymium oxide molded product) can be obtained. Therefore, the type and content of each component in the molded product of the present invention are the same as in the above-mentioned molding composition. The molded and fired product of the present invention (hereinafter sometimes referred to as praseodymium oxide molded and baked product) can be obtained by firing the molded product of the present invention. The β-1,3-glucan contained in the molded product of the present invention may be almost absent by firing.

The praseodymium oxide of the present invention and β-1,3-
A molded article containing one or more molding aids selected from the group consisting of glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds, polyvinyl polymers, etc., or the molded article As the catalyst for decomposing / removing nitrogen oxides, which is a molded and baked product obtained by baking, the praseodymium oxide molded product or the praseodymium oxide molded and baked product obtained above can be used. The above-mentioned praseodymium oxide molded product, which is the main body of the catalyst of the present invention, and the praseodymium oxide molded and baked product are both novel, and the above-mentioned molding praseodymium oxide composition is praseodymium oxide molded product and praseodymium oxide molded and baked product. It is a useful intermediate for the production of products. Hereinafter, the method for producing the molding composition, molded product and molded fired product of the present invention will be described in more detail. The molding praseodymium oxide composition of the present invention comprises praseodymium oxide and β
-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds, one or more molding aids selected from the group consisting of polyvinyl polymers, and optionally other metals It contains an oxide and a catalyst carrier. The praseodymium oxide composition for molding of the present invention is usually used as a wet-solid composition (hereinafter referred to as a kneading solid composition) to which water is added for extrusion molding. In this case, instead of water, a mixture of water and a water-soluble organic solvent such as methanol or ethanol may be used. The amount of these organic solvents may be an appropriate amount. However, it is preferable to use water in the present invention. Also,
The molding praseodymium oxide composition of the present invention may be in a slurry form or another form. The method for preparing the praseodymium oxide composition for molding of the present invention is not particularly limited. For example, if necessary, β-1,3-glucan,
Clay minerals, auxiliaries, etc. are added to praseodymium oxide in powder form, or β-1,3-glucan and, if necessary, auxiliaries are preliminarily added to water or water-soluble substances such as methanol and ethanol. Dissolve it in a small amount of organic solvent, add it to the mixture of praseodymium oxide and clay mineral, then add β-
1,3-glucan, auxiliary agents, clay minerals and the like are sufficiently mixed so as not to be unevenly distributed to form a uniform mixture, and then an appropriate amount of water or an aqueous solution is added to the obtained mixture, which is thoroughly kneaded. A kneading and fixing composition suitable for plastic molding can be obtained. The β-1,3-glucan, clay mineral, and auxiliary agent may be separately mixed with praseodymium oxide.

The praseodymium oxide molded article of the present invention can be produced by any method using the above-described praseodymium oxide composition for molding. For example, it can be molded into a desired shape according to an extrusion molding method, and the temperature can be adjusted to room temperature to 110 ° C. It can be manufactured by drying. Here, after molding the molding praseodymium oxide composition containing water obtained by kneading, when drying the molded product, the molded product is heated in the presence of water to give the heat-coagulability β-1. It is preferable that the 3,3-glucan is thermally coagulated and then dried. Generally, while suppressing free evaporation of water contained in the molded product, if necessary, by heating the molded product in the presence of additional water, the thermosetting β-1,3 -The glucan can be solidified. More specifically, heating by microwaves, heating in a saturated steam atmosphere, heating in a closed container, or the like can be performed. As described above, the temperature at which β-1,3-glucan is heated and coagulated depends on the β-1,3-glucan used, but is usually in the range of 70 to 150 ° C. The heating time is
It is usually about 0.5 to 12 hours. In the case of heating by microwave, it is usually about 10 seconds to 10 minutes. A hollow structure such as a honeycomb structure can also be dried by forcibly passing air. The praseodymium oxide molded article of the present invention can impart strength to the molded article by solidifying the heat-coagulable β-1,3-glucan contained in the molded article, and thus the molded article is dried thereafter. At this time, the molded product does not crack. Drying of the molded product after heat-coagulating the heat-coagulable β-1,3-glucan may be carried out by an ordinary drying method, for example, by allowing it to stand at a high temperature, drying with hot air, or drying at a low temperature. Can be done. In the present invention,
In particular, by firing a molding praseodymium oxide composition containing an inorganic fiber, a fired product having extremely high mechanical strength can be obtained. The praseodymium oxide molded fired product of the present invention can be produced by firing the praseodymium oxide molded product described above. The praseodymium oxide molded product is usually 300 to 800 ° C., preferably 400 to 800 ° C.
Firing is performed at a temperature in the range of 700 ° C. for usually 0.5 to 24 hours, preferably 1 to 5 hours.

Further, the praseodymium oxide compacted and fired product of the present invention is obtained by the method other than the above-mentioned manufacturing method, in which the above-mentioned raw material compound which is transformed into praseodymium oxide by firing, the shaping aid, and, if necessary, a metal other than praseodymium oxide. A molding composition is produced by mixing an oxide (or a raw material compound that is converted to the metal oxide by firing) and / or a catalyst carrier, and the molding composition is molded by extrusion molding. It is also possible to obtain a molded product by the method described above, and then to bake the product. The above-mentioned production method can be carried out according to the above-mentioned method for preparing the molding composition, the molding method, and the firing method. As described above, the molding composition or molded product containing the raw material compound that changes to praseodymium oxide by firing and the molding aid is also a useful production intermediate for producing the molded and fired product of the present invention. The praseodymium oxide molded article and the praseodymium oxide molded and fired article of the present invention obtained as described above have strength not to be cracked by such a manufacturing operation, and excellent nitrogen oxide (particularly NO) decomposition. Since it has a removing activity, it can be used as a catalyst for decomposing and removing nitrogen oxides in exhaust gas and the like. For example, it can be used for exhaust gas treatment from a diesel engine, exhaust gas treatment from a lean burn type gasoline engine, boiler exhaust gas treatment, and the like. The catalyst for decomposition and removal of nitrogen oxides of the present invention is
The above-mentioned praseodymium oxide molded product or praseodymium oxide molded calcined product itself may be used, or a combination of the praseodymium oxide molded product or praseodymium oxide calcined product of the present invention and a known decomposition and removal catalyst for nitrogen oxides, etc. It may be. In the case of producing a praseodymium oxide molded product or a praseodymium oxide molded calcined product that can be used as the catalyst for decomposition and removal of nitrogen oxides of the present invention, it can be molded into any shape and further calcined according to a method known per se. For example, granules, spheres, round bars, square bars,
It can be used as a hollow tube, a thin plate, a sheet, a film, a honeycomb structure or the like. For example, the granular material can be manufactured using a pellet molding apparatus (SE Work Press WPM-10 type and SE soybean, Toyo Hydraulic Machinery Co., Ltd.) or the like. The honeycomb structure can be molded by an extrusion molding method of praseodymium oxide or thallium oxide (for example, an extrusion molding machine, DE-35 type manufactured by Honda Tekko Co., Ltd.). The molded and baked product can be produced by drying the molded product at about 115 ° C and then baking at about 300 to 800 ° C. For example, in the case of granules or spheres, the particle size is not limited as long as it is a practical size, but the normal particle size is 0.
It should be adjusted to 5 to 50 mm, preferably 1 to 20 mm. Further, in the case of a honeycomb structure, it is preferable that the aperture ratio is large. This is because when liquid or gas comes into contact with the zeolite and flows, it can pass without receiving resistance (that is, low pressure loss). The aperture ratio is usually 50 to 90%, preferably 50 to 80%, and more preferably 55 to 80%. The number of cells is usually 10
It is in the range of 600 cells / square inch, preferably 20-400 cells / square inch. Furthermore, the praseodymium oxide composition for molding of the present invention can also be used in a form coated with a wash coat on the surface of a plate such as metal or ceramic, sphere, or honeycomb substrate. In this case, the amount of the praseodymium oxide composition for molding used varies depending on the place of use, the scale of use, etc., and can be appropriately selected according to the purpose.

When the catalyst for decomposing and removing nitrogen oxides of the present invention is used for decomposing and removing nitrogen oxides contained in exhaust gas, the treatment temperature is usually 200 to 700 ° C., preferably 25.
It is in the range of 0 ° C to 600 ° C, more preferably 300 ° C to 500 ° C. In particular, when the catalyst of the present invention contains cobalt oxide (especially Co ₃ O ₄ ) and / or thallium oxide (especially Tl ₂ O ₃ ) in addition to praseodymium oxide, the catalyst has a wide temperature range. Oxides can be decomposed and removed. Gas flow (GHSV) is usually 2,000-
A range of 200,000 h ^-1 is preferred. Furthermore, the catalyst for decomposing / removing nitrogen oxides of the present invention can exhibit an excellent activity for decomposing / removing nitrogen oxides even in the presence of O ₂ . O ₂
When present, the O ₂ concentration is usually 1% to 20%, preferably 5% to 20%. One of the remarkable features of the nitrogen oxide decomposition and removal catalyst of the present invention is that when the conventional nitrogen oxide decomposition and removal catalyst containing praseodymium oxide decomposes and removes nitrogen oxides into nitrogen, carbon monoxide is used. Whereas, the catalyst of the present invention requires a reducing agent such as hydrocarbons,
This is because it is possible to exert an excellent activity of decomposing and removing nitrogen oxides regardless of the presence of reducing agents such as carbon monoxide and hydrocarbons. When a reducing agent is used in the method for decomposing and removing nitrogen oxides of the present invention, carbon monoxide, hydrocarbons and the like can coexist as the reducing agent. Examples of hydrocarbons include olefinic hydrocarbons (eg, methane, ethane, propane, butane), paraffinic hydrocarbons (eg, ethylene, propylene, butene), aromatic hydrocarbons (eg, benzene). , Alicyclic hydrocarbons (eg cyclohexane etc.)
Alternatively, a mixture thereof (for example, kerosene, light oil, heavy oil, etc.) is used. Of these, propane, ethylene, propylene, kerosene, light oil, heavy oil and the like are preferable. Further, organic compounds such as ammonia, urea, alcohols, ethers, and aldehydes can be used instead of the above hydrocarbons or together with the hydrocarbons. When coexisting with hydrocarbons, the hydrocarbons are preferably gas under the temperature conditions in which the catalyst of the present invention and the exhaust gas are in contact, and the addition amount thereof can be appropriately selected depending on the nitrogen oxide concentration in the exhaust gas. However, it is usually 10 to 10,000 ppm, preferably 20 to 6, relative to the exhaust gas.
It is in the range of 000 ppm.

As described above, the praseodymium oxide composition for molding according to the present invention has excellent plastic moldability, and can be molded into a desired shape by, for example, extrusion molding. Accordingly, by firing, it is possible to obtain a praseodymium oxide molded article or a praseodymium oxide molded fired article having excellent strength and dimensional accuracy.
Furthermore, by using the praseodymium oxide composition for molding of the present invention, it is possible to easily obtain a praseodymium oxide molded article having a complicated shape such as a honeycomb structure, which has been difficult in the past, by an extrusion molding method. By firing the praseodymium oxide molded article, a praseodymium oxide molded article having a honeycomb structure can be obtained. The thus-obtained praseodymium oxide molded article and the praseodymium oxide molded and baked article of the present invention thus obtained have an excellent decomposition and removal activity for nitrogen oxides (particularly, a direct decomposition and removal activity for nitrogen oxides). , It can be effectively used as a catalyst for removing nitrogen oxides in gases discharged from ships, aircraft, cogeneration plants, boilers and the like.

[0027]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Reference Example 1 According to the method described in JP-B-48-32573, the fermented liquor was treated with alkali, centrifuged, and then neutralized with an acid to obtain a curdlan solution.
The curdlan solution was desalted and concentrated, dried with a spray dryer and concentrated to obtain curdlan.

[Reference Example 2] 10 g of each of commercially available CoO, Co ₂ O ₃ and Co ₃ O ₄ (Wako Pure Chemical, special grade) was pelletized (SE).
8 mmφ at a pressure of 2 tons using a work press WPM-10 type and SE die manufactured by Toyo Hydraulic Machinery Co., Ltd.
× Molded into pellets with a thickness of 3 mm and in air at 500 ° C
Then, it was fired for 3 hours to obtain fired pellets.

[Reference Example 3] Co ₂ O ₃ (Wako Pure Chemical, 99.5%), Co
₃ O ₄ (Wako Pure Chemical, for chemistry), cobalt oxide (manufactured by Nippon Kagaku Sangyo) and basic cobalt carbonate (manufactured by Nippon Kagaku Sangyo: special cobalt carbonate) 10 g each were pelletized (SE Work Press WPM-10 type and Using SE dice, manufactured by Toyo Hydraulic Machinery Co., Ltd., a pellet of 8 mmφ × thickness 3 mm was formed at a pressure of 2 tons, and the pellet was placed in air for 5
Firing was carried out at 00 ° C. for 3 hours to obtain fired pellets. In the X-ray diffraction pattern after firing, cobalt tetraoxide (Co
₃ O ₄ ) was confirmed.

[Reference Example 4] _{Co (NO 3) 2 · 6H} 2 O ( Wako Pure Chemical) 2
03.7 g was dissolved in 1 liter of pure water. In this solution,
A solution of 85 g of Na ₂ CO ₃ dissolved in 500 ml of water
After dropping at room temperature under stirring for 1 hour, stirring was continued for 1 hour to obtain a cobalt carbonate precipitate. The precipitate was washed, filtered and dried overnight at 100 ° C. 400 in air
The powder was obtained by firing at 3 ° C for 3 hours. 10 g of this powder was molded into a pellet of 8 mmφ × thickness 3 mm at a pressure of 2 tons using a pellet molding device (SE Work Press WPM-10 type and SE die, manufactured by Toyo Hydraulic Machinery Co., Ltd.),
Firing was performed in air at 500 ° C. for 3 hours to obtain a fired pellet.

[0028]

[Reference Example 5] 1400 g (solid content) of basic cobalt carbonate (manufactured by Nippon Kagaku Sangyo Co., Ltd .: special cobalt carbonate, Co content 44.6 wt%, average particle diameter: 1.6 μm), bentonite powder (Mizusawa Chemical Industry) 100 g (solid content) and 400 g (solid content) of kibushi clay (manufactured by Nippon Sheet Glass Co., Ltd., Micrograss chopped strand (RES030)) 100 g
In addition, the curdlan (manufactured by Takeda Pharmaceutical Co., Ltd.,
Piopoly (trade name) -P) 22.0 g, hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd. (Metroze, 90SH100,000) 67.0 g, polyethylene glycol (Sanyo Chemical Co., Ltd., Macrogol)
6000) 11.0 g and this mixture was dry-mixed for about 1 hour using a tabletop twin-screw kneader. Then, distilled water was added to this mixture so that the total amount of water was 580 g, and the mixture was kneaded under reduced pressure (about 100 to 700 mmHg) for about 1 hour. In this kneading, cold water at 5 ° C. was circulated in the jacket of the kneader to cool the kneaded product. The kneaded material thus obtained was placed in a polyethylene bag and kept at room temperature (about 23
Aging). Next, this was kneaded under reduced pressure using an extrusion molding machine (DE-35 type manufactured by Honda Iron Works Co., Ltd.) to obtain a basic cobalt carbonate composition for molding.

[Reference Example 6] A honeycomb forming mold was attached to an extrusion molding machine (DE-35 type manufactured by Honda Iron Works Co., Ltd.), and the same was used as Reference Example 5.
The basic cobalt carbonate composition for molding obtained by
It was molded into a honeycomb molded product having a square of mm and a cell number of 300 cells / square inch. This was cut into a length of 5 cm, heated in a microwave oven for 2 minutes, and then dried in a dryer at 115 ° C. for about 2 hours to obtain a honeycomb formed article of basic cobalt carbonate having an opening ratio of 63%.

Reference Example 7 The molded product obtained in Reference Example 6 was placed in an electric furnace and fired at 700 ° C. for 3 hours to obtain a cobalt oxide honeycomb fired product. In the X-ray diffraction pattern, cobalt trioxide (Co ₃ O ₄ ) was confirmed.

[0029]

Reference Example 8 Cobalt oxide (mixture of CoO and Co ₃ O ₄ , manufactured by Nippon Kagaku Sangyo: cobalt oxide, Co content 72.
4 wt%, average particle size: 6.9 μm), 1400 g (solid content), bentonite powder (Belleclay manufactured by Mizusawa Chemical Industry Co., Ltd.) 100 g (solid content) and Kibushi clay 400 g (solid content) and glass fiber as a firing agent. (Nippon Sheet Glass Co., Ltd.)
Made, Micrograss Chopped Strand (RES03
0)) 100 g, and further, curdlan (Takeda Pharmaceutical Co., Ltd., Piopoly (trade name) -P) 22.0 g and hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd. Metrows, 90SH100,000) 67. 0
g, polyethylene glycol (manufactured by Sanyo Kasei Co., Ltd.,
11.0 g of Macrogol 6000) was added, and this mixture was dry-mixed for about 1 hour using a tabletop twin-screw kneader. Next, distilled water was added to this mixture so that the total amount of water was 620 g, and the mixture was kneaded for about 5 hours. In this kneading, cold water at 5 ° C. was circulated in the jacket of the kneader to cool the kneaded product. The kneaded material thus obtained was placed in a polyethylene bag and aged for 1 day at room temperature (about 23 ° C.). Next, this was kneaded under reduced pressure using an extrusion molding machine (DE-35 type manufactured by Honda Iron Works Co., Ltd.) to obtain a cobalt oxide composition for molding.

[Reference Example 9] A honeycomb forming mold was attached to an extrusion molding machine (DE-35 type manufactured by Honda Iron Works Co., Ltd.), and this was used to prepare Reference Example 7
The cobalt oxide composition for molding obtained in 1 above was molded into a honeycomb molded product having a square shape of 30 mm on a side and having 300 cells / square inch. This was cut into a length of 5 cm, heated in a microwave oven for 2 minutes, and then dried in a dryer at 115 ° C. for about 2 hours to obtain a cobalt oxide honeycomb molded product having an opening ratio of 63%.

Reference Example 10 The molded product obtained in Reference Example 9 was placed in an electric furnace and fired at 700 ° C. for 3 hours to obtain a honeycomb fired product of cobalt oxide. In the X-ray diffraction pattern, cobalt trioxide (Co ₃ O ₄ ) was confirmed.

[Reference Example 11] Measurement of NO decomposition removal activity in the presence of propylene The granular material obtained in Reference Example 2 was used as a catalyst. For the reaction, an atmospheric pressure fixed bed flow reactor (CAT-4000, manufactured by Best Sokki Co., Ltd.) was used. 10 g of three kinds of cobalt oxide were filled in each cell, and the reaction gas flow rate was 6.67 liters /
Flow at a reaction temperature of 200 to 500 ° C., and the inlet gas and outlet gas before and after the cell are chemiluminescent NOx meter (BCL-51
1AS, manufactured by Best Sokki Co., Ltd.) and a gas chromatograph. As the reaction gas, NO: 1000 pp
_{m, C 3 H 6: 1000ppm} , O 2: 10%, H 2 O: 1
A mixed gas of 0%: N ₂ balance was used. [Table 1] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction in the presence of propylene in each of the cobalt oxide fired pellets.

[Table 1] From Table 1, it can be seen that the burned products of CoO and Co ₃ O ₄ have a large amount of O ₂
It can be seen that even in the presence, it exhibits excellent NO decomposition removal activity.

[0030]

[Reference Example 12] Measurement of NO decomposition removal activity in the absence of propylene An atmospheric fixed bed flow reactor was charged with 10 g of the four types of cobalt oxide calcined pellets obtained in Reference Example 3 and the reaction gas flow rate was 6 It was allowed to flow at 0.67 l / min at a reaction temperature of 200 to 500 ° C., and the inlet gas and the outlet gas of the catalyst layer were analyzed using a chemiluminescence type NOx meter and a gas crocotograph. The reaction gas is NO: 1000 ppm, O ₂ : 1
A mixed gas of 0%, H ₂ O: 10% and diluted with N ₂ was used. [Table 2] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of each cobalt oxide fired pellet in the absence of propylene.

[Table 2] From Table 2, it was confirmed that each cobalt oxide calcined pellet directly decomposes NO in the presence of O ₂ even under the condition that propylene is not present. Furthermore, the same test was performed using the fired pellets obtained in Reference Example 4, and the results are shown in [Table 3].

[Table 3] From Table 3, it was confirmed that the calcined pellets obtained in Reference Example 4 directly decomposed NO in the presence of O ₂ even under the condition that propylene does not exist.

Reference Example 13 The cobalt oxide honeycomb formed article obtained in Reference Example 9 was fired at various temperatures of 400 to 700 ° C. for 3 hours to obtain a cobalt oxide honeycomb formed article. This cobalt oxide honeycomb formed and fired product was cut into a diameter of 20 mmφ and a length of 30 mm, and the mixture was filled in a normal pressure fixed flow reactor.
The NO conversion was determined under the same conditions as in Reference Example 12. NO in the NO reduction reaction of each cobalt oxide honeycomb molded fired product
The reaction temperature dependence of the conversion rate of is shown in [Table 4].

[Table 4] From Table 4, the cobalt oxide honeycomb molded fired product obtained by firing the cobalt oxide honeycomb formed product obtained in Reference Example 9 was obtained in the presence of O ₂ even in the absence of a reducing agent.
It was confirmed that NO was directly decomposed.

Reference Example 14 The cobalt carbonate honeycomb formed article obtained in Reference Example 6 was fired at various temperatures of 400 to 700 ° C. for 3 hours to obtain a cobalt oxide honeycomb formed article. The NO conversion was determined by the same method as in Reference Example 12. [Table 5] shows the reaction temperature dependence of the NO conversion rate in the NO reduction reaction of each cobalt oxide honeycomb molded fired product.

[Table 5] From Table 5, the cobalt carbonate honeycomb formed body obtained by firing the cobalt carbonate honeycomb formed body obtained in Reference Example 6 and NO in the presence of O ₂ even under the condition that the reducing agent does not exist
Was confirmed to be directly decomposed.

[0031]

[Reference Example 15] 10 g of commercially available thallium oxide (Tl ₂ O ₃ ; Wako Pure Chemical Industries, special grade) was used in a pellet molding apparatus (SE work press WPM-10 type and SE die, manufactured by Toyo Hydraulic Machinery Co., Ltd.). 8 mmφ x thickness 3 at a pressure of 2 tons
mm pellets and fired in air at 500 ° C. for 3 hours to obtain thallium oxide fired pellets.

[Reference Example 16] Measurement of NO decomposition removal activity in the presence of propylene The thallium oxide calcined pellets obtained in Reference Example 15 were used as a catalyst. For the reaction, an atmospheric pressure fixed bed flow reactor (CAT-4000, manufactured by Best Sokki Co., Ltd.) was used. 10 g of each of the three kinds of granular materials was filled in each cell, the reaction gas was passed at a flow rate of 6.67 liters / minute and a reaction temperature of 150 to 500 ° C., and the inlet gas and the outlet gas before and after the cell were chemiluminescent NOx meters ( BCL-511AS, manufactured by Best Sokki Co., Ltd.) and a gas chromatograph. As the reaction gas, N
O: 1000 ppm, C ₃ H ₆ : 1000 ppm, O ₂ :
A mixed gas of 10%, H ₂ O: 10% and N ₂ balance was used. [Table 6] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of thallium oxide calcined pellets in the presence of propylene.

[Table 6] Next, in [Table 7], conversion rates of C ₃ H ₆ to CO and CO ₂ are shown.

[Table 7] From the results of [Table 6] and [Table 7], it was revealed that the fired thallium oxide pellets of the present invention have excellent NO decomposition activity. Further, it was suggested that the fired thallium oxide pellets of the present invention directly decompose NO even under the condition that propylene (C ₃ H ₆ ) which is a reducing agent does not exist. In order to make this point clearer, the following Reference Example 1
7 was carried out.

[Reference Example 17] Measurement of NO decomposition removal activity in the absence of propylene An atmospheric fixed bed flow reactor was charged with 10 g of the thallium oxide calcined pellets obtained in Reference Example 15, and the reaction gas flow rate was 6.67 liters. / Min, the reaction temperature was 200 to 500 ° C, and the inlet gas and the outlet gas of the catalyst layer were analyzed using a chemiluminescence type NOx meter and a gas chromatograph. As the reaction gas, NO: 1000 ppm, O ₂ :
A mixed gas diluted with 10%, H ₂ O: 10%, N ₂ was used. [Table 8] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of the thallium oxide fired pellets in the absence of propylene.

[Table 8] From the results in [Table 8], it was confirmed that the fired thallium oxide pellets of the present invention directly decompose NO even under the condition that propylene as a reducing agent does not exist.

[0032]

[Example 1] 10 g of commercially available praseodymium oxide (Pr ₆ O ₁₁ , Wako Pure Chemical Industries, special grade) was used in a pellet molding apparatus (SE Work Press WPM-10 type and SE die, manufactured by Toyo Hydraulic Machinery Co., Ltd.). It was molded into a pellet having a diameter of 8 mm and a thickness of 3 mm at a pressure of 2 tons, and was fired in air at 500 ° C. for 3 hours to obtain a praseodymium oxide fired pellet.

Example 2 Commercially available praseodymium nitrate (praseodymium (III) nitrate n hydrate; Pr (NO ₃ ) ₃ .nH ₂ O (n = 4
~ 6)) powder, 435 g was dissolved in pure water to make the total volume 2 liters. Next, while stirring this solution, a 1N NaOH solution was added dropwise at room temperature to obtain a yellow-green praseodymium oxide precipitate. The NaOH solution was added dropwise until no formation of precipitate was observed and then left overnight with stirring. The precipitate is then washed and filtered, 10
Dry overnight at 0 ° C. The dried precipitate is crushed and then calcined in air at 400 ° C for 3 hours to obtain black praseodymium oxide.
About 170 g of (Pr ₆ O ₁₁ ) powder was obtained. 10 g of this powder was used with a pellet molding machine (SE Work Press WPM-10 type and SE die, manufactured by Toyo Hydraulic Machinery Co., Ltd.).
It was molded into a pellet having a diameter of 8 mm and a thickness of 3 mm at a pressure of 2 tons, and the pellet was fired in air at 500 ° C. for 3 hours to obtain a praseodymium oxide fired pellet.

[Example 3] 10 g of a commercially available industrial praseodymium oxide (Nikki Co., Ltd., Pr ₆ O ₁₁ content 96.9 wt%) was used in a pellet molding apparatus (SE Work Press WPM-10 type and SE die, Toyo Hydraulic Machinery Co., Ltd.). Made into pellets of 8 mmφ × thickness of 3 mm with a pressure of 2 tons,
It was fired in air at 500 ° C. for 3 hours to obtain praseodymium oxide fired pellets.

Example 4 1400 g (solid content) of praseodymium oxide for industrial use (manufactured by Nikki Co., Ltd., content of Pr ₆ O _{11 is} 96.9 wt%), and 100 g of bentonite powder (Beleclay manufactured by Mizusawa Chemical Industry Co., Ltd.) as a sintering agent ( Solid content) and Kibushi viscosity of 400 g (solid content), glass fiber (Nippon Sheet Glass Co., Ltd., Micrograss chopped strand (RE)
S030)) 100 g, and further curdlan (manufactured by Takeda Pharmaceutical Co., Ltd., Biopoly (trade name) -P) 22.0
g and hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metroses, 90SH100,00)
0) 67.0 g and polyethylene glycol (manufactured by Sanyo Chemical Industry Co., Ltd., Macrogol 6000) 11.0 g were added, and this mixture was dry-mixed for about 1 hour using a tabletop twin-screw kneader.
Next, distilled water was added to this mixture so that the total amount of water was 550 g, and the mixture was kneaded under reduced pressure (about 100 to 700 mmHg) for about 1 hour. In this kneading, cold water at 5 ° C. was circulated in the jacket of the kneader to cool the kneaded product.
The kneaded material thus obtained was placed in a polyethylene bag and aged for 1 day at room temperature (about 23 ° C.). Next, using an extruder (DE-35 type manufactured by Honda Iron Works Co., Ltd.),
The mixture was kneaded under reduced pressure to obtain a praseodymium oxide composition for molding.

[0033]

[Example 5] A honeycomb molding die was mounted on an extrusion molding machine (DE-35 type manufactured by Honda Iron Works Co., Ltd.) and was used in Example 4
30 m on each side of the praseodymium oxide composition for molding obtained in
It was molded into a honeycomb molded product having a square of m and 300 cells / square inch. Cut this to a length of 5 cm, heat it in the microwave for 2 minutes, and then about 2 in a dryer at 115 ° C.
After drying for an hour, a honeycomb molded product of praseodymium oxide having an opening ratio of 63% was obtained.

Example 6 The molded product obtained in Example 5 was placed in an electric furnace and fired at 500 ° C. for 3 hours to obtain a honeycomb fired product of praseodymium oxide.

[Test Example 1] Measurement of NO decomposition removal activity in the presence of propylene The praseodymium oxide calcined pellets obtained in Examples 1 and 2 were used as a catalyst. For the reaction, an atmospheric pressure fixed bed flow reactor (CAT-4000, manufactured by Best Sokki Co., Ltd.) was used. Three
10 g of each kind of granular material was filled in each cell, the reaction gas flow rate was 6.67 liter / min, and the reaction temperature was 150-50.
It was allowed to flow at 0 ° C., and the inlet gas and the outlet gas before and after the cell were analyzed using a chemiluminescence type NOx meter (BCL-511AS, manufactured by Best Instruments Co., Ltd.) and a gas chromatograph. As the reaction gas, NO: 1000 ppm, C ₃ H ₆ : 1000 pp
A mixed gas of m, O ₂ : 10%, H ₂ O: 10% and N ₂ balance was used. [Table 9] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of each praseodymium oxide fired pellet in the presence of propylene.

[Table 9] Next, in [Table 10], conversion rates of C ₃ H ₆ to CO and CO ₂ are shown.

[Table 10] From the results of [Table 9] and [Table 10], it became clear that the praseodymium oxide calcined pellets of the present invention have excellent NO decomposition activity. Further, the praseodymium oxide fired pellets of the present invention are propylene (C ₃ H ₆ ) which is a reducing agent.
It was suggested that NO was directly decomposed even in the absence of. In order to make this point clearer, the following test example 2 was carried out.

[0034]

Test Example 2 Measurement of NO Decomposition / Removal Activity in the Absence of Propylene 10 g of each of the praseodymium oxide calcined pellets obtained in Examples 1 and 2 was filled in an atmospheric fixed bed flow reactor.
Flow rate of reaction gas is 6.67 l / min, reaction temperature is 200
The mixture was allowed to flow at ˜500 ° C., and the inlet gas and the outlet gas of the catalyst layer were analyzed using a chemiluminescence type NOx meter and a gas chromatograph. As the reaction gas, NO: 1000 pp
A mixed gas diluted with m, O ₂ : 10%, H ₂ O: 10%, and N ₂ was used. [Table 11] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of each praseodymium oxide fired pellet in the absence of propylene.

[Table 11] From the results in [Table 11], it was confirmed that the praseodymium oxide fired pellets of the present invention directly decompose NO even under the condition that propylene as a reducing agent does not exist.

[Test Example 3] Measurement of NO decomposition removal activity in the presence of propylene The praseodymium oxide calcined pellets obtained in Example 3 were used as a catalyst. For the reaction, an atmospheric pressure fixed bed flow reactor (CAT-4000, manufactured by Best Sokki Co., Ltd.) was used. 10 g of the fired pellets prepared in Example 3 was filled in a cell, the reaction gas was flowed at 6.67 l / min, and the reaction temperature was 150 to 500.
The gas was allowed to flow at 0 ° C, and the inlet gas and the outlet gas before and after the cell were analyzed using a chemiluminescence type NOx meter (BCL-511AS, manufactured by Best Instruments Co., Ltd.) and a gas chromatograph. As the reaction gas, NO: 1000 ppm, C ₃ H ₆ : 1000 ppm,
A mixed gas of O ₂ : 10%, H ₂ O: 10% and N ₂ balance was used. [Table 12] shows the reaction temperature dependence of NO conversion and C ₃ H ₆ conversion into CO and CO ₂ in the NO reduction reaction of praseodymium oxide calcined pellets prepared in Example 3 in the presence of propylene. .

[Table 12] From the results in [Table 12], it was suggested that the praseodymium oxide sintered pellets of the present invention decompose NO even in the presence of propylene which is a reducing agent, but the reducing agent is not necessarily involved in the reaction. In order to make this point clearer, in Test Example 4, the NO decomposition activity in a system without propylene was measured.

[0035]

Test Example 4 Measurement of NO Decomposition / Removal Activity in the Absence of Propylene An atmospheric fixed bed flow reactor was charged with 10 g of the praseodymium oxide pellets obtained in Example 3 and the reaction gas flow rate was 6.67 liters. / Min, reaction temperature 200-500 ° C
And the inlet gas and outlet gas of the catalyst layer were analyzed using a chemiluminescence type NOx meter and a gas chromatograph. As the reaction gas, NO: 1000 ppm, O ₂ :
A mixed gas diluted with 10%, H ₂ O: 10%, N ₂ was used. [Table 13] shows the reaction temperature dependence of the conversion rate of NO in the NO reduction reaction of praseodymium oxide fired pellets in the absence of propylene.

[Table 13] From the results of [Table 13], it was confirmed that the praseodymium oxide fired pellets of the present invention directly decompose NO even in a system in which propylene as a reducing agent does not exist.

[Test Example 5] The praseodymium oxide honeycomb fired product obtained in Example 6 was cut into a diameter of 20 mmφ and a length of 30 mm, and the mixture was filled in a fixed-pressure fixed bed flow reactor, and the NO conversion rate was the same as in Test Example 4. I asked. The reaction temperature dependence of the NO conversion in the NO reduction reaction in the absence of propylene was shown in Table 14 for the praseodymium oxide honeycomb fired product.
It was shown to.

[Table 14] From Table 14, it was confirmed that the praseodymium oxide honeycomb calcination product obtained in Example 6 directly decomposes NO even under the condition that propylene as a reducing agent does not exist.

[0036]

The molding praseodymium oxide composition for molding according to the present invention has excellent plastic moldability, and can be molded into a desired shape by, for example, extrusion molding, which is dried and, if necessary, calcined. By doing so, it is possible to obtain a praseodymium oxide molded product and a praseodymium oxide molded baked product that are excellent in strength and dimensional accuracy. The molded product and molded fired product of the present invention can exhibit excellent decomposition and removal activity of nitrogen oxides even when a reducing agent such as carbon monoxide or hydrocarbon is not present.
It can be used as a catalyst for decomposition and removal of nitrogen oxides discharged from cogeneration plants, boilers and the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 35/04 ZAB 301 P B01D 53/36 102 H

Claims (14)

[Claims] 1. A catalyst for decomposing and removing nitrogen oxides, which comprises praseodymium oxide alone as a catalyst component. 2. One or more molding aids selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds and polyvinyl polymers. A catalyst for decomposing / removing nitrogen oxides, which is a molded product containing: and a molded and baked product obtained by baking the molded product. 3. The catalyst for decomposing / removing nitrogen oxides according to claim 1, which is a honeycomb structure. 4. The catalyst for decomposition and removal of nitrogen oxides according to claim 1, wherein nitrogen oxides are directly decomposed and removed in the absence of a reducing agent. 5. One or more molding aids selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydroxy compounds and polyvinyl polymers. A molding composition comprising: 6. One or more molding aids selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds and polyvinyl polymers. And a molded article containing. 7. The molded product according to claim 6, which is a honeycomb structure. 8. A molded and baked product obtained by baking the molded product according to claim 6 or 7. 9. A method for decomposing and removing nitrogen oxides, which comprises bringing the catalyst for decomposing and removing nitrogen oxides according to claim 1 into contact with nitrogen oxides. 10. The method for decomposing and removing nitrogen oxides according to claim 9, which is carried out in the absence of a reducing agent. 11. The method for decomposing and removing nitrogen oxides according to claim 9, which is carried out in the presence of O ₂ . 12. One or more molding aids selected from the group consisting of praseodymium oxide and β-1,3-glucan, clay minerals, inorganic fibers, cellulosic compounds, polyhydric hydroxy compounds and polyvinyl polymers. 6. The method for producing a molding composition according to claim 5, characterized in that 13. The method for producing a molded article according to claim 6 or 7, wherein the molding composition according to claim 5 is extruded. 14. The method for producing a molded and fired product according to claim 8, wherein the molded product according to claim 6 or 7 is fired.