JPH0331495B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a porous sheet or honeycomb catalyst structure for gas phase catalytic reduction of nitrogen oxides in the presence of ammonia. In general, a catalyst with a honeycomb structure (hereinafter sometimes simply referred to as a honeycomb catalyst) has many passages parallel to the flow of gas to be reacted, and therefore does not cause a large pressure drop when passing through the catalyst structure. Therefore, it is advantageously used when treating a large amount of gas with a high linear velocity, for example, in the removal of nitrogen oxides contained in exhaust gas from boilers, internal combustion engines, nitric acid plants, etc. by vapor phase catalytic reduction. Furthermore, the honeycomb catalyst has the advantage that by selecting the diameter of the passages, dust contained in the gas can pass through without being deposited in the catalyst structure. Such honeycomb catalysts have conventionally been manufactured by various methods. Currently, the most widely used method is to extrude an aqueous slurry of ceramic materials such as cordierite, mullite, clay, etc. from a mold directly into a honeycomb structure, which is then dried.
After sintering, a carrier and a catalytically active material (hereinafter, the carrier and catalytically active material may be collectively referred to simply as a catalytic material) are applied, dried, and fired.
However, in this method, the ceramic substrate as described above is generally inert and has poor affinity for water, so it is difficult to support a sufficient amount of catalyst material to carry out the catalytic reaction. , it is necessary to repeat the steps of applying the catalyst material to the substrate, drying, and sintering, thus making the manufacturing cost of the catalyst high, and furthermore, the sintered substrate does not contain the catalyst material. The supported catalyst material is likely to peel off from the surface of the catalyst structure during the required gas phase reaction. In order to solve the above-mentioned problems, another method is known in which honeycomb catalysts are manufactured by extruding a clay consisting of the catalytic material itself. Although this method has the advantage of excellent durability because the catalyst material is uniformly and integrally incorporated into the catalyst structure, it requires a large amount of catalyst material, so the resulting catalyst structure is very poor. It is expensive.
Furthermore, in order for the resulting catalyst structure to have the required mechanical strength, the clay is usually extruded under high pressure, resulting in the resulting catalyst structure having a low porosity and therefore a low catalytic activity. Furthermore, a problem common to both of the above-mentioned methods is that the honeycomb catalyst made of ceramic material is heavy and therefore has various difficulties in handling. Thus, a honeycomb catalyst has been proposed which is lighter and easier to handle than the honeycomb catalyst structure made of ceramic material as described above. For example, Japanese Unexamined Patent Publication No. 53-55051 discloses a honeycomb catalyst in which a honeycomb substrate is a multilayer corrugated cardboard structure made of asbestos fiber sheets, and a catalyst material is supported on the honeycomb base. However, similar to the ceramic substrate, this catalyst structure has extremely low catalytic activity because the substrate made of asbestos fiber lacks the so-called carrier effect, which is the action of a carrier material that increases the catalytic activity of the catalytically active substance. In addition, the base made of asbestos fiber sheet is
In order to deposit a sufficient amount of catalytic material, as in the case of ceramic substrates, the asbestos substrate must be repeatedly dipped or impregnated with the catalytic material, so that the coating of catalytically active material that is formed is The coating is thick and therefore prone to cracking during the step of baking with the substrate after such immersion or impregnation. If a concentrated slurry or solution of the catalytic material is used, there is no need to repeatedly immerse or impregnate the catalytic material, but on the other hand, it is difficult to uniformly support the catalytic material on the substrate. Therefore, the object of the present invention is to provide a material consisting of inorganic fibers,
It has a small bulk specific gravity, is lightweight and easy to handle,
Furthermore, it is an object to provide a highly porous sheet or honeycomb-like catalyst structure in which the catalyst material is evenly distributed and supported. Therefore, it is also an object of the present invention to provide a porous catalyst structure with improved catalytic activity and durability due to the excellent diffusion of the gas to be reacted into the catalyst structure. The present invention provides a method for producing a porous sheet or honeycomb-like catalyst structure for gas phase catalytic reduction of nitrogen oxides in the presence of ammonia, which comprises (a) ceramic fibers, silica fibers, silica-alumina fibers, chrysotile fibers, At least one inorganic fiber selected from asbestos fibers, rock wool, glass fibers, anthophyllite fibers, potassium titanate fibers, and carbon fibers, and having an average fiber length of 1 to 20 mm and an average diameter of 0.1 to 30 μm. is beaten in water to form an aqueous slurry with a solid content of 0.1 to 10% by weight, (b) a sheet with a porosity of 65 to 80% is formed from this aqueous slurry, and (c) a sheet made from or made from this sheet. An impregnating slurry containing titanium oxide or a precursor thereof which can be converted into titanium oxide by firing as a carrier at a concentration of at least 100 g/m and having a viscosity of 5 to 250 cps at room temperature is added to the honeycomb structure. (d) the sheet or honeycomb structure is then impregnated, dried and optionally fired;
immersed in an aqueous immersion solution in which at least one catalytically active substance selected from copper, iron, vanadium, tungsten, and molybdenum oxides or a precursor thereof that can be converted into the oxide by calcination is dissolved, and dried; It is characterized by being fired. The inorganic fiber used in the present invention is a fiber that can be beaten and is preferably stable at a temperature of at least about 200°C, preferably has a diameter of about 0.1 to 30 μm, and a fiber length of about It is 1 to 20 mm. The inorganic fiber is at least one selected from ceramic fiber, silica fiber, silica-alumina fiber, chrysotile fiber, asbestos fiber, rock wool, glass fiber, anthophyllite fiber, potassium titanate fiber, and carbon fiber, but especially , ceramic fibers, alumina fibers, silica-alumina fibers, and asbestos fibers are preferably used because they have excellent formability into sheets and honeycomb structures. Furthermore, if necessary, heat-resistant organic fibers such as polytetrafluoroethylene fibers may also be used in combination with the above-mentioned inorganic fibers. The fibers used are selected, on the one hand, taking into account the conditions of the gas-phase catalytic ring reaction of the nitrogen oxide-containing gas, in particular the reaction temperature. For example, if the reaction temperature is approximately
Ceramic fibers and asbestos fibers are preferably used when the reaction temperature is below 500℃.
When the temperature is 500 to 1000°C, silica fibers and silica-alumina fibers are preferably used. Furthermore, in the present invention, combustible organic fibers that burn and disappear upon firing can also be used in combination with the above-mentioned inorganic fibers. The above combustible fibers include:
Examples include rayon fibers, cellulose fibers, vinylon fibers, polypropylene fibers, polyethylene fibers, acrylic fibers, polyester fibers, etc., but are not limited to these. By using such combustible fibers, the porosity of the sheet or honeycomb structure can be adjusted, and the mechanical strength of the sheet made from the aqueous fiber slurry can be increased, so that the honeycomb structure described below can be improved. It is possible to improve the molding processability. Preferably, the combustible organic fibers have a fineness of 3 denier or less, a fiber length of about 3 to 10 mm, and a fiber length of about 1 to 30 mm based on the inorganic fibers.
% by weight, most preferably in the range of 2-20% by weight. Inorganic fibers and optionally organic fibers are beaten in water to form a stock from which these fibers can be made into paper. Here, the stock is prepared so that the solids content, ie, fiber, is 1 to 10% by weight, preferably 2 to 6% by weight. Note that sheets made of inorganic fibers and mixtures of inorganic fibers and organic fibers, as well as methods for producing such fiber sheets, are already known in the field of paper manufacturing technology, so a description of the beating of such fibers and paper making will be omitted here. . According to the method of the invention, the fiber slurry preferably contains additives known in the papermaking art, such as binders, adhesion promoters, sizing agents, etc., as described below. The fiber slurry further contains titanium oxide or a precursor thereof that can be converted to titanium oxide by calcination, such as titanium hydroxide,
It can be uniformly dispersed and supported in the substrate as a carrier in advance in the sheet or honeycomb structure to be formed. The titanium oxide or its precursor added to the fiber slurry preferably has a particle size of 0.01 to 0.01 so that the titanium oxide or its precursor can be fixed to the fibers in the slurry with good yield.
50 μm, particularly preferably 0.1 to 10 μm. In this way, even when the paper stock contains solid titanium oxide or its precursor, the solid content of the paper stock, that is, the amount of fibers and titanium oxide or its precursor, is suitably 1 to 10% by weight. And this solid content is preferably
It consists of titanium oxide or its precursor in an amount of 40% by weight or less, particularly preferably 30% by weight or less, and fibers in an amount of 60% by weight or more, particularly preferably 70% by weight or more. If the carrier material in the solid content exceeds 40% by weight, it is difficult to form a highly porous sheet, and therefore it is difficult to uniformly disperse and support the catalyst material in the sheet or honeycomb structure. It becomes difficult to form the sheet into a honeycomb structure, and it does not have the mechanical strength necessary for forming the sheet into a honeycomb structure. As mentioned above, the paper stock preferably contains a binder. The binder is added in an amount ranging from 0.01 to 10% by weight based on the solids content in the fiber slurry. Binders that can be used in the present invention are not particularly limited, but include, for example, inorganic binders such as alumina sol, silica sol, titania sol, acrylonitrile-butadiene rubber (NBR)
Examples include organic binders such as latexes of synthetic rubbers such as rubber and styrene-butadiene rubber (SBR). The stock may further contain a fixing agent and/or a sizing agent. As the fixing agent, for example,
Organic cationic polymer electrolytes are preferably used. Specific examples include polyacrylamine, polyamine, polyamine and polyamide epichlorohydrin condensation polymers, polyethyleneimine, and the like. The above polyamines include condensates of alkylene dichloride and alkylene polyamines such as ethylene diamine, tetraethylene diamine and hexaethylene diamine, and poly(N,N-
dimethyl- and diethylamino methacrylate),
polyvinylimidazoline, polyvinylpyridine,
It includes a cyclized polymer of diallylamine, a copolymer of N-vinylpyrrolidone and acrylamide, etc. Inorganic adhesion promoters such as aluminum sulfate and iron sulfate are also used. The amount of fixing agent in the stock is preferably about 1 to 10% by weight based on the weight of the carrier or its precursor that the stock contains. Stocks also have sizing agents based on solids content.
It can be contained in an amount of 0.01 to 1% by weight. As the sizing agent, for example, an organic silicone polymer such as rosin or polysiloxane is used. More specifically, and by way of example only, the stock is prepared as follows. The fibers are beaten in water to form an aqueous fiber slurry, optionally titanium oxide or its precursor is added and mixed, and then, after optionally a fixing agent and/or sizing agent is added, a slurry such as sulfuric acid is added. Add mineral acid to bring the pH of the slurry to about 3-6, preferably 4.
Adjust to ~5. If no fixing agent is used in stock preparation, the fiber slurry is preferably prepared to have a PH of about 6-8. Finally, if necessary, after adding a binder to the fiber slurry, the solids content is adjusted to 1 to 10% by weight, preferably 2 to 6% by weight, so as to be suitable for paper making. The stock thus prepared is then made into sheets by a conventional paper machine, such as a cylinder paper machine, a fourdrinier paper machine, a short wire paper machine, etc. Alternatively, the paper stock may be made using a hand-sintered net. The sheet thus produced is usually dried at a temperature of about 60 to 150°C. However, this drying temperature is not limited at all; for example, when the paper stock is made of fibers with a high melting point, it may be dried at a higher temperature. According to the method of the invention, it is necessary that such a sheet or a honeycomb structure made from it, on which the catalyst material is to be supported, have a porosity of 60 to 85%. Here, the porosity (%) is defined by the following formula. (1-apparent specific gravity of the sheet or honeycomb/true specific gravity of the sheet or honeycomb)×100 Note that the apparent specific gravity of the honeycomb means the apparent specific gravity of the wall body made of sheets forming the honeycomb structure. In connection with the above, forming a sheet from the stock containing said combustible organic fibers and firing this sheet or a honeycomb structure made therefrom;
By eliminating combustible fibers, the porosity of the sheet or honeycomb structure can be controlled. According to the method of the present invention, the sheet produced as described above or the honeycomb structure produced therefrom is first impregnated with an aqueous slurry (hereinafter, this aqueous slurry) containing titanium oxide or its precursor as a carrier. (referred to as a slurry), dried, and optionally calcined to convert the precursor to active titanium oxide. However, the sheet or honeycomb structure does not necessarily need to be fired at this stage; for example, a catalytically active substance or its precursor is supported on a sheet or honeycomb structure supported by a carrier as described later, and then fired. You may. The impregnating slurry needs to contain titanium oxide or its precursor at a concentration of at least 100 g/m, and further needs to have a viscosity of 5 to 250 cps at room temperature. Preferably, the concentration of titanium oxide or its precursor in the impregnation slurry is 100 to 1000 g/g/. That is, one feature of the method of the present invention is that the sheet or honeycomb structure has a porosity of 60 to 85% as described above, and that the sheet or honeycomb structure has a high concentration of titanium oxide or its precursor as described above. The impregnated slurry is impregnated with a low viscosity while containing a large amount of water, so that the slurry easily penetrates into the porous substrate and is thus substantially uniformly dispersed throughout the substrate. Therefore, if the viscosity of the impregnating slurry is greater than 250 cps at room temperature, it will be difficult to penetrate into the substrate even when the substrate has a large porosity as described above, and thus the substrate will have limited porosity. The carrier is supported only on the surface layer, and the resulting catalyst structure has low catalytic activity and poor durability. Titanium oxide is produced by the so-called sulfuric acid method, which is widely known as one of the methods for producing titanium oxide.
Normally, titanium oxide contains 7 to 15% by weight of free sulfate ions in terms of sulfuric acid, but when the present inventors prepared the impregnation slurry using such titanium oxide, the content of free sulfate ions was It has been found that free sulfate ions significantly increase the viscosity of the impregnated slurry. Therefore, in the method of the present invention,
In preparing the impregnation slurry, it is preferable to use titanium oxide that does not substantially contain free sulfate ions or has a reduced content of free sulfate ions. To obtain such titanium oxide, for example, a metatitanic acid cake obtained as an intermediate in the production of titanium oxide by the sulfuric acid method is treated with an aqueous solution of a water-soluble barium salt, such as barium chloride or barium nitrate, to remove the free sulfuric acid in the metatitanic acid. The ions are immobilized as water-insoluble barium salts, and the metatitanic acid is then calcined, preferably at a temperature in the range of 300-600°C for 1-5 hours. The titanium oxide obtained by such a method does not substantially contain free sulfate ions, or the content thereof is significantly reduced, and at the same time, its specific surface area remains extremely large. The effect of having a large specific surface area will be described later. Alternatively, for example, metatitanic acid may be treated with aqueous ammonia to cause free sulfate ions to form water-soluble ammonia salts, which are eluted from the metatitanic acid cake by washing with water. Thereafter, the metatitanic acid cake is baked under the same conditions as in the above method. Also by this method, it is possible to obtain titanium oxide that does not substantially contain free sulfate ions or has a significantly reduced content of free sulfate ions. The titanium oxide thus obtained preferably contains at most 4% by weight of free sulphate ions, based on the titanium oxide. Furthermore, the titanium oxide obtained in this way is
Another feature is that the specific surface area is between 50 and 150 m ² /g. Even by calcining commercially available conventional titanium oxide from the sulfuric acid process at high temperatures, e.g. 1000°C or higher, it contains virtually no free sulfate ions or its content is significantly reduced. However, the titanium oxide obtained in this way has a specific surface area of about 10
m ² /g or less, and therefore, such titanium oxide has almost no carrier effect. On the other hand, the impregnating slurry used in the method of the present invention contains titanium oxide with a high specific surface area at a high concentration and, as mentioned above, has an extremely low viscosity at room temperature. The catalytic structure obtained by impregnating this with a catalytically active substance and further supporting a catalytically active substance has a high catalytic activity as a result of the high supporting effect of the carrier uniformly dispersed and supported in the substrate. According to the method of the present invention, the sheet or honeycomb structure is impregnated with the impregnation slurry containing titanium oxide or its precursor as a carrier material as described above, and then impregnated with a catalytically active material or by calcination. It is immersed in a solution, usually an aqueous solution (hereinafter referred to as immersion solution), containing dissolved precursors that can be converted into catalytically active substances. The viscosity of the dipping solution at room temperature is much lower than that of the impregnating slurry, and although the substrate is already impregnated with or supported on the carrier or its precursor, it does not have sufficient porosity for the dipping solution to penetrate. Furthermore, the dipping solution penetrates well into the substrate so that the catalytically active material is substantially uniformly dispersed throughout the substrate. This sheet or honeycomb structure can then be dried to obtain the catalyst structure according to the invention. When the immersion solution is a solution of a precursor of a catalytically active substance, the substrate immersed in such a solution must then be calcined to convert said precursor into a catalytically active substance. The catalytically active substance used in the method of the present invention is
At least one selected from oxides of copper, iron, vanadium, tungsten, and molybdenum or a precursor that can be converted into such an active substance by calcination. Such precursors include, for example, water-soluble vanadium oxalate and metatungstic acid, which upon calcination form vanadium pentoxide in the former and tungsten trioxide in the latter as catalytically active substances. The sheet or honeycomb structure is dried after being impregnated with the impregnating slurry and/or after being immersed in the dipping solution, respectively. The drying temperature is not particularly limited, but is preferably in the range of room temperature to 200° C. at any stage.
Similarly, after dispersing the support material titanium dioxide precursor or catalytically active material precursor in the sheet or honeycomb structure, the temperature at which they are fired is preferably in the range of 300 to 600°C; It usually lasts 1 to 5 hours. If the sheet or honeycomb structure contains the above-mentioned combustible organic fibers, the above-mentioned firing burns and eliminates the fibers, increasing the porosity of the substrate. Therefore, the porosity of the substrate can be adjusted by adjusting the amount of combustible organic fiber added at the stage of preparing the paper stock. For example, if the sheet or honeycomb structure is fired before loading the carrier material, a porous substrate with a high porosity can be obtained.
A large amount of carrier material can be supported more easily, and thus the amount of carrier material supported can be adjusted. Furthermore, if the substrate is fired after supporting the catalytically active substance, the porosity of the catalyst structure, and therefore the
The diffusivity of the reactant gas into the catalyst structure can be adjusted. The impregnation slurry may also contain from 1 to 10 parts by weight of the same fibers used in preparing the paper stock per 100 parts by weight of carrier. By including fibers in the impregnation slurry in this way, the mechanical strength and durability of the resulting catalyst structure can be improved. In particular, it not only increases the adhesion strength of the catalytic material to the substrate and the resistance to peeling due to scratching, but also prevents the catalytic material from cracking, which often appears when the catalytic substrate is dried or fired. Fibers for the above purposes are
Preferably, the length is about 0.5 to 5 mm and the diameter is about 0.1 to 30 μm. In the present invention, the term "honeycomb structure" includes all structures known as honeycomb structures in catalyst technology, and the manufacturing method thereof is not particularly limited. However, a multilayer corrugated structure is one type of honeycomb structure that can be preferably used in the present invention. A catalyst having such a honeycomb structure is usually held in a basket and filled into a reactor so that the flow channels of the honeycomb structure are parallel to the flow direction of the process gas. The honeycomb structure of the present invention can also be constructed by spirally winding a single-sided corrugated board made from a sheet obtained by the method of the present invention and adhering the peaks to the liner on the back side of the adjacent corrugated board. can. Furthermore, the honeycomb structure of the present invention can also be constructed by arranging the sheets of the present invention in parallel to each other at appropriate intervals in a basket or frame. For gas phase catalytic reduction of nitrogen oxides using the catalyst structure according to the invention, the stoichiometric amount required to convert the nitrogen oxides into nitrogen and water is applied to a gas containing nitrogen oxides, e.g. exhaust gas from a boiler. Ammonia in an amount of 0.5 to 10 times the theoretical amount is added as a reducing agent, and the mixed gas is heated at a temperature of 150 to 650°C, preferably
It is passed through the catalyst structure at 200-550° C. and an areal velocity of 5-50 Nm ³ /m ² ·h. The pressure at which the gas phase reaction is carried out is not particularly limited, but is usually in the range from normal pressure to about 10 kg/cm ² . As described above, in the sheet or honeycomb-shaped catalyst structure according to the present invention, the titanium oxide as a carrier and the catalytically active substance are substantially uniformly supported within the structure. It has improved catalytic activity and durability in gas phase catalytic reduction reactions of nitrogen oxides using ammonia as a reducing agent. This is in sharp contrast to conventional catalyst structures in which the catalytically active material is supported only in a limited area near the surface. More specifically, the catalyst structure according to the invention still has a large porosity even after loading the carrier and the catalytically active substance as described above, so that the reaction gas can easily diffuse into such a structure. The catalytic activity is much higher than that of conventionally known catalyst structures. Furthermore, according to the catalyst structure of the present invention, the catalyst material is substantially uniformly dispersed and supported over the entire structure, so that even if a portion of the catalyst material is peeled off by, for example, dust in exhaust gas, The structure as a whole still maintains high catalytic activity, and therefore maintains high catalytic activity over a long period of time. Particularly, according to the present invention, a porous sheet or a porous honeycomb structure made from the same is first impregnated with an aqueous slurry containing titanium dioxide or its precursor, i.e., a carrier material, and these are uniformly dispersed. After this, the sheet or honeycomb structure is immersed in a solution containing the catalytically active substance or its precursor to uniformly disperse and support the catalytic substance, thereby obtaining a catalytic structure, which significantly improves its durability. . That is, although exhaust gas from boilers and the like generally contains a large amount of dust as well as nitrogen oxides, the catalyst structure of the present invention maintains high catalytic activity over a long period of time. On the other hand, a porous sheet or a honeycomb structure obtained from the porous sheet is impregnated with a slurry in which a catalytically active material is dissolved while a carrier material is dispersed, and thus a carrier material and a catalytically active material are simultaneously supported. Although the reason for the catalyst structure is not necessarily clear,
The activity per supported catalytic active substance is low, and when exhaust gas containing dust is treated, the catalytic activity quickly decreases over time. In particular, in preparing the impregnating slurry, a preferred method according to the present invention is adopted which substantially removes free sulfate ions contained in the titanium dioxide used or significantly reduces its content and maintains a high specific surface area. The slurry thus obtained is impregnated into a porous sheet or honeycomb structure to support the carrier material, and then
By supporting a catalytically active substance, a porous catalyst structure having higher catalytic activity and durability can be obtained. The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. A Preparation Example of Catalyst Structure 1 Ceramic fibers with an average diameter of approximately 3 μm and an average fiber length of approximately 10 mm (Fine Flex manufactured by Nichias Co., Ltd.)
1300) 1.5Kg is beaten in 30℃ of water to form an aqueous fiber slurry, and this slurry has an average particle size of approximately 2μ.
m, 500 g of anatase titanium dioxide with a specific surface area of 80 m ² /g was added together with 10 g of a cationic polymer electrolyte (Lufax 295 manufactured by Rohm and Haas),
Next, sulfuric acid was added to adjust the pH of the slurry to about 4.5, and 1 g of an acrylonitrile-butadiene copolymer latex binder (Nipole 1571, manufactured by Nippon Zeon Co., Ltd.) was added to fix titanium dioxide to the fibers. The paper stock thus obtained was made into a sheet using a hand-made net and dried. This sheet has a thickness of 0.3mm.
The basis weight was 140 g/m ² . The sheet was processed into single-sided corrugated board using a conventional corrugated board processing machine using silica sol as an adhesive. This single-sided corrugated board was laminated and bonded using a silica sol adhesive to obtain a multilayered corrugated board with a honeycomb structure. This structure had a volume of 86 ml, a porosity of 68%, and a contact surface area of 860 x 10 ^-2 cm ² /cm ³ . Incidentally, the above-mentioned contact surface area means the surface area of a structure with which gas can come into contact in a gas phase contact reaction. Aqueous ammonia was added to the metatitanic acid cake obtained as an intermediate for producing titanium dioxide by the sulfuric acid method to neutralize it, the cake was washed with water, and ammonia sulfate was eluted into the water and removed from the metatitanic acid.
After this, the cake was baked at a temperature of 450℃ for 3 hours.
Titanium dioxide having a specific surface area of 80 m ² /g and containing 0.8% by weight of free sulfate ions as sulfuric acid was obtained. This titanium dioxide 180g, silica sol 144ml
A mixture of 288 ml of water and 288 ml of water was ground in a ball mill for 5 hours to obtain an impregnated slurry containing 375 g of titanium dioxide and having a viscosity of 19 cps at room temperature. The honeycomb structure obtained above was wash-coated with this impregnation slurry, dried, and fired at 450° C. for 3 hours to obtain a honeycomb-like carrier structure supporting 12.50 g of titanium dioxide. The honeycomb-like support structure obtained above was then immersed in an aqueous solution containing 95 g/vanadyl oxalate as vanadium pentoxide, dried and calcined for 3 hours at a temperature of 450° C. to obtain a catalyst structure according to the present invention. Ta. It supports a total of 13.13 grams of a catalyst material of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5. Therefore, the amount of catalyst material supported per unit contact surface area is 2.65×10 ⁻² g/cm ² . Example 2 1.5 kg of the same ceramic fiber as in Example 1 was beaten in 30 g of water with 120 g of rayon fiber of 1.5 denier and average fiber length of 5 mm. The paper stock thus obtained was made into a sheet in the same manner as in Example 1 and dried. The sheet had a thickness of 0.3 mm and a basis weight of 80 g/m ² . This sheet was processed into a honeycomb structure having the same volume and contact surface area as in Example 1 and a porosity of 76%. The same metatitanic acid used in Example 1 was treated with barium chloride to fix 40% of the free sulfate ions as barium sulfate, and calcined at a temperature of 450°C for 3 hours to give a specific surface area of 97 m ² /g and free Titanium dioxide containing 3.2% by weight of sulfate ions in terms of sulfuric acid was obtained. A mixture of 180 g of titanium dioxide, 195 ml of silica sol, and 265 ml of water was ground in a ball mill for 5 hours.
Titanium dioxide content 360g/, viscosity at room temperature
An impregnated slurry of 68 cps was obtained. The honeycomb structure obtained above is added to this impregnation slurry.
After washing, drying and firing for 3 hours at a temperature of 450° C., a honeycomb-like carrier structure carrying 20.31 g of titanium dioxide was obtained. The honeycomb-like carrier structure obtained above was then immersed in an aqueous solution containing 115 g/vanadyl oxalate as vanadium pentoxide for 10 minutes, dried,
After calcination for 3 hours at a temperature of 0.degree. C., a catalyst structure according to the invention was obtained. This is a total amount of catalyst materials of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5.
Carrying 21.33g. Therefore, the amount of catalyst material supported per unit contact surface area is 2.88×10 ⁻² g/cm ² . Example 3 500 g of asbestos fibers with an average diameter of about 8 μm and an average length of about 2 mm were beaten in 20% water, and the resulting aqueous fiber slurry had an average particle diameter of about 0.5 μm and a specific surface area of about
After adding 175 g of anatase titanium dioxide (50 m ² /g), aqueous ammonia was added to form a slurry.
The pH was adjusted to 8. Add to this slurry the above
0.7 g of Lufax 295 was added and sulfuric acid was added to adjust the pH of the slurry to approximately 4. Then 1g of Nipole
1571 was added to fix titanium dioxide to the fibers. The paper stock thus obtained was made into a sheet using a handmade net in the same manner as in Example 1 and dried. This sheet had a thickness of 0.3 mm and a basis weight of 230 g/cm ² . This sheet was processed into a honeycomb structure having the same volume and contact surface area as Example 1, but with a porosity of 62%. A mixture of 180 g of titanium dioxide, 144 ml of silica sol, and 288 ml of water, which was the same as that used to prepare the impregnated slurry in Example 1, was ground in a ball mill for 1 hour to obtain an impregnated titanium dioxide content of 375 g/1 and a viscosity of 19 cps at room temperature. Got slurry. The honeycomb structure obtained above was wash-coated with this impregnation slurry, dried and heated at a temperature of 450℃ for 3 hours.
After firing for a period of time, a honeycomb-like carrier structure supporting 13.01 g of titanium dioxide was obtained. Next, 22 g/vanadyl oxalate in terms of vanadium pentoxide and 22 g/in terms of tungsten trioxide.
The honeycomb-like support structure obtained above was immersed in an aqueous solution containing 176 g of metatungstic acid for 10 minutes, dried and calcined at a temperature of 450°C for 3 hours to obtain titanium dioxide as the support and pentoxide as the catalytically active substance. A catalyst structure according to the invention was obtained supporting a catalyst material consisting of vanadium and tungsten trioxide.
This catalyst structure supports a total amount of 21.46 g of titanium dioxide, vanadium pentoxide, and tungsten trioxide in a weight ratio of 91:1:8. Therefore, the amount of catalyst material supported per unit contact surface area is 2.90×10 ^-2 g/
^cm2 . Example 4 Ceramic fiber (Nichias Co., Ltd. Fine Flex 1300) with an average diameter of about 3 μm and a length of about 20 mm, 1.5 kg
and 180 g of rayon fiber of 1.5 denier and average fiber length of 5 mm in 30 ml of water. The obtained paper stock was made into a dry sheet in the same manner as in Example 1. This sheet had a thickness of 0.3 mm and a basis weight of 71 g/cm ² . This sheet was processed into a honeycomb structure having the same volume and contact surface area as in Example 1 and a porosity of 82%. The same metatitanic acid used in Example 1 was treated with barium chloride to fix 20% of the free sulfate ions as barium sulfate, and calcined at a temperature of 450°C for 3 hours to give a specific surface area of 115 m ² /g and free Titanium dioxide containing 3.8% by weight of sulfate ions in terms of sulfuric acid was obtained. A mixture of 180 g of titanium dioxide, 195 ml of silica sol, and 265 ml of water was ground in a ball mill for 5 hours.
Titanium dioxide content 360g/, viscosity at room temperature
An impregnated slurry of 110 cps was obtained. The honeycomb structure obtained above is coated with this impregnation slurry.
Wash coated, dried and calcined for 3 hours at a temperature of 450° C. to obtain a honeycomb-like support structure carrying 20.49 g of titanium dioxide. Next, the honeycomb-shaped carrier structure obtained above was immersed in an aqueous solution containing 120 g/vanadyl oxalate in terms of vanadium pentoxide for 10 minutes, dried, and
℃ temperature for 3 hours to form a catalyst material consisting of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5.
A honeycomb-like catalyst structure was obtained in which a total amount of 21.65 g of catalyst material was supported and the amount of catalyst material supported per unit contact surface area was 2.93×10 ⁻² g/cm ² . Example 5 350 g of asbestos fibers with an average diameter of about 8 μm and an average fiber length of about 2 mm, and 350 g of asbestos fibers with an average diameter of about 6 μm and a length of about 5 mm.
150 g of glass fiber (E glass manufactured by Nittobo Co., Ltd.) was beaten in 20 g of water. Then 1g of Nipole
1571 was added. The obtained paper stock was made into a sheet in the same manner as in Example 1 and dried. The sheet is 0.3 thick
mm, and the basis weight was 135 g/cm ² . This sheet was processed in the same manner as in Example 1 into a honeycomb structure having the same volume and contact surface area and a porosity of 69%. The same metatitanic acid used in Example 1 was neutralized by adding ammonia water to remove free sulfate ions, and calcined at a temperature of 450°C for 3 hours to determine the specific surface area.
Anatase type titanium dioxide containing 87 m ² /g and 1.4% by weight of free sulfate ions in terms of sulfuric acid was obtained. An impregnating slurry containing this titanium dioxide in a content of 385 g/3 and having a viscosity of 35 cps at room temperature was prepared in the same manner as above, and the honeycomb structure obtained above was washed and coated twice with this impregnating slurry, It was dried and calcined at a temperature of 450° C. for 3 hours to obtain a honeycomb-like carrier structure supporting 21.24 g of titanium dioxide. Next, the honeycomb-shaped carrier structure obtained above was immersed in an aqueous solution containing 115 g/vanadyl oxalate in terms of vanadium pentoxide for 10 minutes, dried, and
℃ temperature for 3 hours to form a catalyst material consisting of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5.
A honeycomb-like catalyst structure was obtained in which a total amount of 22.30 g of catalyst material was supported and the amount of catalyst material supported per unit contact surface area was 2.87×10 ⁻² g/cm ² . Comparative Example 1 Porous metal sheet with a thickness of 1.5 mm (Sumitomo Electric Industries, Ltd.
Co., Ltd.) is processed into a corrugated structure and laminated to create a volumetric
A honeycomb structure of 173 ml and a contact surface area of 427×10 ⁻² cm ² /cm ³ was obtained. 171 g of the same titanium dioxide used to prepare the impregnation slurry in Example 1, 9 g of vanadyl oxalate (as vanadium pentoxide) and water.
Grind 288ml in a ball mill for 5 hours and store at room temperature.
An impregnated slurry of 25 cps was obtained. The honeycomb structure obtained above was wash coated with this impregnation slurry, dried and heated at a temperature of 450°C for 3
Calcined for a time, the total amount of titanium dioxide and vanadium pentoxide catalyst material is 13.82g in a weight ratio of 95:5.
A honeycomb-like catalyst structure was obtained in which the amount of catalyst material supported per unit contact surface area was 3.76×10 ⁻² g/cm ² . Comparative Example 2 A commercially available honeycomb structure made of sintered ceramic oxide having a volume of 76 ml, a wall thickness of 0.33 mm, a pitch of 3.75 mm, and a unit contact surface area of 973×10 ^-2 cm ² /cm ³ (Nippon Spark Plug Co., Ltd.) Co., Ltd.) was washed and coated three times with the same impregnation slurry used in Comparative Example 1.
Next, the treatment was carried out in the same manner as in Comparative Example 1, and the catalyst materials of titanium dioxide and vanadium pentoxide were mixed in a weight ratio of 95:5.
A honeycomb-like catalyst structure was obtained in which a total amount of 14.15 g of catalyst material was supported and the amount of catalyst material supported per unit contact surface area was 2.28×10 ⁻² g/cm ² . Comparative Example 3 Titanium dioxide 180 containing 8.2% by weight of free sulfate ions in terms of sulfuric acid and having a specific surface area of 130 m ² /g
A mixture of 195 ml of silica sol and 265 ml of water was ground in a ball mill for 5 hours to obtain a titanium dioxide content of 360 ml.
An impregnated slurry having a viscosity of 897 cps at room temperature was obtained. The same honeycomb structure with a porosity of 76% as used in Example 2 was washed with this impregnation slurry.
It was coated, dried and fired at a temperature of 450° C. for 3 hours to obtain a honeycomb-like carrier structure supporting 24.63 g of titanium dioxide. This support structure was then treated as in Example 2 to obtain a total amount of 25.87 g of catalytic material consisting of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5.
A honeycomb-like catalyst structure was obtained in which the amount of catalyst material supported per unit contact surface area was 3.48×10 ⁻² g/. Comparative Example 4 180 g of titanium dioxide and 195 ml of silica sol, containing 3.2% by weight of free sulfate ions in terms of sulfuric acid and having a specific surface area of 97 m ² /g, were used to prepare the impregnation slurry in Example 2. 47 ml of an aqueous solution containing 200 g/vanadium oxalate in terms of vanadium pentoxide and 218 ml of water were ground in a ball mill for 5 hours to prepare an impregnated slurry having a viscosity of 77 cps at room temperature. The same honeycomb structure with a porosity of 76% as used in Example 2 was washed with this impregnation slurry.
Coating, drying, and calcining at a temperature of 450°C for 3 hours to support a total of 23.70 g of a catalyst material of titanium dioxide and vanadium pentoxide in a weight ratio of 95:5,
The amount of catalyst material supported per unit contact surface area is 3.2×
A honeycomb-like catalyst structure with a weight of 10 ⁻² g/cm ² was obtained. B. Catalyst Evaluation Figures 1, 2, and 3 show titanium oxide in the thickness direction of the wall of the catalyst structure measured by an X-ray microanalyzer in the honeycomb catalyst structures obtained in Examples 1, 2, and 3, respectively. shows the distribution of
It is clear that the titanium oxide is substantially uniformly distributed throughout the catalyst structure. FIG. 4 shows the same titanium oxide distribution as above for the catalyst structure obtained in Comparative Example 3. It is clear that because the titanium oxide slurry used has a high viscosity, titanium dioxide is supported only on a limited surface layer of the catalyst structure. Next, the catalytic activity of each catalyst structure obtained in the above Examples and Comparative Examples to convert nitrogen oxides into nitrogen and water in the presence of a reducing agent ammonia was evaluated. That is, each catalyst structure is filled in a Pyrex glass tube with an inner diameter of 50 mm, which is wrapped with an insulating material to maintain a constant internal temperature, and the catalyst structure is filled with nitrogen monoxide.
200ppm, ammonia 200ppm, water vapor 10% by weight,
A mixed gas consisting of 12% carbon dioxide by volume, 1000ppm sulfur dioxide, and residual nitrogen was heated at a temperature of 350℃ and an area velocity.
It was passed at 20Nm ³ /m ² ·hr. The conversion rate of nitric oxide (NO) is defined by the following formula. Conversion rate = [(NO concentration at reactor inlet) - (NO concentration at reactor outlet)] / (NO concentration at reactor inlet)] x 100
(%) The results are shown in Table 1. Additionally, to evaluate the durability of the catalyst structure, each catalyst structure was rapidly heated to a temperature of 450°C in an electric furnace.

[Table] Amount per ^cm2 .
After that, the catalyst structure was immediately taken out from the electric furnace and allowed to cool to room temperature. After repeating this operation to give a thermal history 10 times, the catalyst structure is placed in a shaker.
After shaking for 15 minutes, the weight of the catalytic material exfoliated from the catalytic structure was measured. The results are shown in Table 1. Furthermore, in order to clarify the difference in durability between the catalyst structures of Example 2 and Comparative Example 4, each catalyst structure was packed into a reactor, and 100 ppm of nitrogen monoxide, 1% by weight of oxygen, and 10% by weight of water vapor were added to the reactor. A mixed gas consisting of , sulfur dioxide 50 ppm, residual nitrogen, and dust content of 100 mg/Nm ³ was heated at a temperature of 350°C and an area velocity of 20 N.
It passed through at m ³ /m ² ·hr. The results are shown in Table 2.

[Table] As is clear from the results in Table 1, the catalyst structures of Comparative Examples 1 and 3 had a higher catalytic activity than the catalyst structure of the present invention, despite having a larger amount of catalyst material supported per unit contact surface area. Also, comparative example 1
The catalyst structures of and 2 are less durable than the catalyst structure according to the invention. Furthermore, as is clear from Table 2, the catalyst structure of Comparative Example 4 is inferior to the catalyst structure of Example 2 when considering the amount of carrier supported per unit contact surface area, and has a significantly lower catalytic activity. Poor wear resistance.

[Brief explanation of the drawing]

Embodiment 1 of the present invention is shown in FIGS. 1 to 3, respectively.
Fig. 4 shows the distribution diagram of titanium dioxide in the thickness direction of the wall of the honeycomb-shaped catalyst obtained in Examples 2 and 3 by an X-ray microanalyzer, and Fig. 4 similarly shows the distribution diagram of the titanium dioxide obtained in Comparative Example 3.
The distribution diagram of titanium dioxide in the catalyst structure is shown.

Claims (1)

[Claims] 1. A method for producing a porous sheet or honeycomb-like catalyst structure for catalytic reduction of nitrogen oxides in the presence of ammonia, comprising: (a) ceramic fibers, silica fibers, silica-alumina fibers, At least one type selected from chrysotile fibers, asbestos fibers, rock wool, glass fibers, anthophyllite fibers, potassium titanate fibers, and carbon fibers, with an average fiber length of 1 to 20 mm and an average diameter of 0.1 to 30 μm. Beating certain inorganic fibers in water to form an aqueous slurry with a solids content of 0.1 to 10% by weight, (b) forming a sheet with a porosity of 65 to 80% from this aqueous slurry, (c) forming this sheet or At least 100 g of titanium oxide as a carrier is added to the honeycomb structure produced from this, and the content of free sulfuric acid is 4% by weight or less in terms of sulfuric acid based on titanium oxide, and the specific surface area is 50 to 150 m ² /g. (d) Then, the sheet or honeycomb structure is impregnated with an impregnating slurry containing a concentration of
immersed in an aqueous immersion solution in which at least one catalytically active substance selected from copper, iron, vanadium, tungsten, and molybdenum oxides or a precursor thereof that can be converted into the oxide by calcination is dissolved, and dried; A method for producing a catalyst structure for reducing nitrogen oxides, which comprises firing. 2 Titanium oxide or a precursor that can be converted to titanium oxide by firing is added to the aqueous slurry to make the solid content of the aqueous slurry 1 to 10% by weight, and this solid content is 60% by weight or more of fibers and titanium oxide. 2. The method for producing a catalyst structure for reducing nitrogen oxides according to claim 1, wherein the catalyst structure comprises 40% by weight or less of a nitrogen oxide or a precursor thereof. 3. Production of a catalyst structure for reducing nitrogen oxides according to claim 1 or 2, characterized in that an aqueous slurry is formed by beating inorganic fibers together with 1 to 30% by weight of combustible fibers. Method. 4 The concentration of titanium oxide in the impregnation slurry is
The method for producing a catalyst structure for reducing nitrogen oxides according to claim 1, wherein the amount is in the range of 100 to 1000 g/.