JPH0114807B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing a catalyst for removing nitrogen oxides, and more specifically, it not only maintains high nitrogen oxide removal activity over a long period of time even under severe usage conditions, but also has a method for producing a catalyst for removing sulfur dioxide. The present invention relates to a method for producing a catalyst for removing nitrogen oxides, which has an extremely low rate of oxidation of sulfur trioxide to sulfur trioxide. Conventional technology Generally, it is already known that fired titanium oxide products are used as catalyst carriers or catalysts, but surface area, crystal shape, heat resistance, mechanical strength after molding, etc. have important effects on the carrier or catalyst function. Since it differs depending on the manufacturing method and the presence/absence, type, amount, etc. of additive substances, various manufacturing methods have been proposed in the past. For example, if silica is added to titanium oxide and fired, the resulting fired product will generally have a larger surface area and improved heat resistance. According to a method in which silica is added to titanium salts such as, neutralized and hydrolyzed, and the titanium hydroxide thus produced is calcined to form titanium oxide, the titanium hydroxide produced by hydrolysis is There is a problem that it tends to become titanic acid, and therefore, when it is calcined, it tends to become rutile-type titanium oxide, which is unsuitable as a carrier or a catalyst. On the other hand, it is already known that if titanium salt is thermally hydrolyzed, it will easily become metatitanic acid, and if this is calcined, it will give anatase titanium oxide, which is generally the preferred crystalline form for carriers and catalysts, although there are other factors as well. It is being However, according to the method of adding silica to titanium hydroxide or titanium oxide obtained in this way and firing it, it is difficult to obtain a mixture with a uniform composition, and especially when silica is added to titanium hydroxide. In some cases, since titanium hydroxide is in the form of a gel, silica cannot be uniformly dispersed in titanium hydroxide, making it impossible to obtain a high-performance support or catalyst. Problems to be Solved by the Invention The present invention has been made in order to solve the various problems described above. It is an object of the present invention to provide a method for producing a high-performance catalyst for removing nitrogen oxides using a fired titanium oxide product as a carrier, which has excellent strength after molding. Means for Solving the Problems The method for producing a catalyst for removing nitrogen oxides according to the present invention involves adding fine particles of silicic acid to titanium sulfate, thermally hydrolyzing it, drying and firing, and adding vanadium to the thus obtained fired product. , tungsten, molybdenum,
It is characterized by supporting an oxide of at least one element selected from copper, iron, chromium, manganese and cerium. Preferably, in this method, titanium sulfate is thermally hydrolyzed in the presence of particulate silicic acid, After converting the generated metatitanic acid into a sol,
Filtration, drying, and firing to obtain a titanium oxide fired product.
Using this as a carrier, the above oxide is supported. The fine particle silicic acid used in the present invention is also known as white carbon, and one of its characteristics is that it has a very large specific surface area. These fine particles of silicic acid may be produced by either a wet method or a dry method, and in the present invention, ordinary commercially available products can be used. Commercial products of fine particle silicic acid that can be suitably used in the present invention include, for example, "Fine Seal" (registered trademark, manufactured by Tokuyama Soda Co., Ltd.) and "Aerosil" (registered trademark, manufactured by Nippon Aerosil Co., Ltd.). Among these, those with an average particle size of 10 to 50 mμ,
Those having a specific surface area of 200 to 300 m ² /g are preferably used. The amount of particulate silicic acid added is 5 to 50% by weight based on titanium oxide, and when it is less than 5% by weight, the effect of improving the carrier or catalyst performance by adding particulate silicic acid in the fired product is small; On the other hand, when it exceeds 50% by weight, the content of titanium oxide becomes relatively low, and when this is used as a carrier, the performance of the carrier and catalyst based on titanium oxide deteriorates, which is not preferable. In the method of the present invention, the above-mentioned fine particles of silicic acid are added to an aqueous titanium sulfate solution, and this mixture is thermally hydrolyzed to produce metatitanic acid, which is precipitated with fine particles of silicic acid. In the present invention, thermal hydrolysis of titanium sulfate is
The aqueous solution containing finely divided silicic acid is usually heated to 80%
C. to its boiling point, preferably at the boiling point. More preferably, the thermal hydrolysis is carried out in the presence of seed crystals in order to reduce the time required for thermal hydrolysis of titanium sulfate. For example, colloidal metatitanic acid particles of about 2% by weight in terms of titanium oxide are added as seed crystals. It is already known that metatitanic acid is produced by thermally hydrolyzing titanium sulfate, but since this metatitanic acid is in the form of a gel, in the present invention, titanium sulfate is preferably produced in the presence of fine particles of silicic acid. After thermal hydrolysis with
Even finer particles of silicic acid can be uniformly dispersed in metatitanic acid. The method of solization is not particularly limited, and for example, the reaction mixture obtained by thermal hydrolysis is washed with water to remove most of the sulfuric acid groups, and then hydrochloric acid or nitric acid is added to partially or completely solize the mixture. Or
In particular, if sulfate radicals are not removed by washing with water, add alkaline earth metal chlorides such as barium chloride, strontium chloride, and calcium chloride, or alkaline earth metal nitrates such as barium nitrate, strontium nitrate, and calcium nitrate to the reaction mixture. and fixing the sulfate radical as a water-insoluble barium salt while partially or completely solizing the reaction mixture.
The amount of these gelling agents added is appropriately selected depending on the degree to which the reaction mixture is to be turned into a sol. The mixture of metatitanic acid and particulate silicic acid obtained in this way is washed with water, filtered, dried, then calcined at a temperature of 800°C or less, preferably 700 to 200°C, and pulverized to form a powder. Obtain a baked product with a shape.
In this case, according to the present invention, metatitanic acid obtained by thermally hydrolyzing titanium sulfate is used, so it contains a sulfate group, even if only in a small amount, and this also results in anatase-type titanium oxide, which is preferable as a carrier or catalyst in calcination. This is one of the causes. In addition, when using the powdered fired product as a carrier in a predetermined shape such as a honeycomb shape, the dried product obtained by drying the above mixture may be processed by any conventionally known method, such as extrusion molding or rolling granulation. It may be baked after being molded by a method such as the above. It is also possible to add an appropriate amount of water to the above powdered fired product, knead it, mold it into a desired shape, and then fire it again. In this case, after forming into the desired shape, it may be fired again at a temperature of 800°C or lower, preferably 700 to 200°C. In this manner, according to the present invention, a fired titanium oxide product as a molded product can also be obtained. In addition, in the present invention, in any of the above cases, if a metatitanic acid sol or gel is newly added to the powdered dried product or fired product, the product is molded into the desired shape, and then fired, the mechanical strength and porosity,
Various physical properties such as specific surface area and pore distribution can be improved, and the shrinkage rate during firing can be suppressed. In such cases, the amount of metatitanic acid sol or gel added is 5 to 50% of the weight of the molded product in terms of titanium oxide.
Weight % is appropriate. Furthermore, it is of course possible to use conventionally known general molding aids such as methyl cellulose during molding. In the present invention, the firing atmosphere is not limited at all, and may be air, combustion gas, inert gas, or the like. The fired titanium oxide product obtained as described above is not limited in any way by theory, but
Due to the presence of fine particles of silicic acid, the crystal growth of titanium oxide is suppressed during firing of metatitanic acid, and the ungrown anatase-type crystals remain, resulting in a fired product with a large surface area and excellent heat resistance. It has excellent mechanical strength after molding and can be suitably used as a catalyst carrier. As shown in Figure 1, it is confirmed that the fired product remains ungrown anatase by its X-ray spectrum showing low and broad peaks. In the case of anatase type titanium oxide, as shown in the X-ray spectrum of FIG. 2, the peak is high and sharp because the crystals have grown extremely well. According to the method of the present invention, the calcined titanium oxide product obtained as described above is used as a carrier, and an oxide conventionally known to have catalytic activity for removing nitrogen oxides is supported on this carrier. Due to the unexpected synergistic effect with the oxides constituting the fired product, it is possible to obtain a catalyst for removing nitrogen oxides having excellent selective catalytic reduction activity of nitrogen oxides using ammonia as a reducing agent. The method for supporting the above-mentioned oxide on the titanium oxide fired product can be any method conventionally used for preparing catalysts. For example, the above-mentioned oxide or its precursor is supported on the fired product formed into a predetermined shape. After impregnating or coating with the solution or dispersion contained therein, it may be fired to a predetermined temperature as necessary. Of course, the catalyst for removing nitrogen oxides of the present invention can also be produced by kneading the powdered calcined product with the solution or dispersion, molding it into a desired shape, and then calcining it to a predetermined temperature as necessary. Obtainable. In order to remove nitrogen oxides from a gas mixture containing nitrogen oxides using the catalyst according to the present invention, the amount of nitrogen oxides contained in the gas mixture is 0.5 to 5 times the mole, preferably 1 to 2 times the mole of nitrogen oxides contained in the gas mixture. Ammonia is added and passed through a reaction bed filled with catalyst.
Any of a moving bed, a fluidized bed, a fixed bed, etc. can be used as the reaction bed. Since the catalyst for removing nitrogen oxides according to the method of the present invention contains fine silicic acid particles and has excellent heat resistance, the reaction temperature may range from 200 to 600°C, but preferably from 300 to 500°C. It is. Further, the space velocity of the gas is in the range of 1000 to 100000 hr ^-1 , preferably 3000 to 300000 hr ^-1 . The catalyst according to the invention can be used for the treatment of any gas containing nitrogen oxides, but in particular boiler exhaust gas, i.e. 100-1000 ppm nitrogen oxides, mainly carbon monoxide, as well as 200-2000 ppm
sulfur oxides, mainly sulfur dioxide, 1-10
% oxygen by volume, 5-20% carbon dioxide by volume, 5-20
It can be suitably used to remove nitrogen oxides from exhaust gas containing % by volume of water vapor. Effects of the Invention According to the method of the present invention, as described above, in the production of a fired titanium oxide product as a carrier, fine particles of silicic acid are added to titanium sulfate, and this is thermally hydrolyzed to convert metatitanic acid into fine particles of silicic acid. Because of coprecipitation, the fine particles of silicic acid are uniformly dispersed in the resulting mixture, and when this is fired, the titanium oxide remains in ungrown anatase crystals due to the action of the fine particles of silicic acid. The resulting fired product has a large surface area, and because the fine particles of silicic acid are uniformly dispersed in the titanium oxide, its heat resistance is significantly improved.
It also has excellent mechanical strength after molding. The catalyst for removing nitrogen oxides according to the method of the present invention is
Since the fired product is used as a carrier and metal oxides having catalytic activity for removing nitrogen oxides are supported, a synergistic effect between these metal oxides and anatase-type titanium oxide and fine particle silicic acid whose growth has been suppressed is achieved. This not only maintains high nitrogen oxide removal activity over a long period of time even under severe usage conditions, but also has an extremely low oxidation rate of sulfur dioxide to sulfur trioxide, making it suitable for practical and industrial nitrogen oxidation. Excellent as a catalyst for removing substances. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 1 kg of titanium sulfate solution obtained from the titanium oxide manufacturing process using the sulfuric acid method was taken out as titanium oxide, and 200 g of fine particle silicic acid "Fine Seal" (registered trademark, manufactured by Tokuyama Soda Co., Ltd.) was added thereto and sufficiently After stirring and mixing, the mixture was heated to its boiling point to thermally hydrolyze titanium sulfate and co-precipitate it with fine particles of silicic acid. This precipitate was filtered, washed with water, dried at 100°C for 12 hours, and then calcined at a temperature of 500°C for 3 hours. This calcined product was pulverized using a sample mill, the particle size was adjusted, and the product was used as a support for the following catalyst for removing nitrogen oxides. 250 ml of a 10% methylamine solution containing 110 g of ammonium paratungstate in the above powder carrier
was added and kneaded, and then extruded into a lattice-shaped molded product using an extruder, heated from room temperature to 100°C to dry, and then fired at 500°C for 3 hours to form a nitrogen oxide supporting tungsten oxide. A catalyst for removal was obtained. Example 2 A carrier was produced in exactly the same manner as in Example 1, except that "Aerosil" (registered trademark, manufactured by Nippon Aerosil Co., Ltd.) was used as the fine particle silicic acid, and Example 1 was added to the carrier. A catalyst for removing nitrogen oxides was obtained by supporting tungsten oxide in exactly the same manner as above. Example 3 The coprecipitate of metatitanic acid and fine-particle silicic acid obtained in Example 1 was filtered, washed with water, and then dispersed in water again. 80 g of barium chloride (dihydrate) was added thereto, and metatitanic acid The mixture was made into a sol and thoroughly stirred and mixed. Thereafter, in the same manner as in Example 1, the precipitate was filtered, washed with water, dried at 100°C for 12 hours, and then heated to 500°C.
The mixture was calcined at a temperature of 3 hours, and then pulverized using a sample mill to obtain a carrier. The X-ray spectrum of the carrier thus obtained is shown in FIG. It is clear that the peak is low and broad, and the anatase crystal remains ungrown. The X-ray spectrum was measured using an X-ray diffractometer RAD-A manufactured by Rigaku Denki Co., Ltd., and the measurement conditions were as follows. Scanning speed 1°/4 minutes full scale 1000cps Time constant 1 second Chart speed 10mm/min Target Copper tube voltage 30KV Tube current 10mA For comparison, the X-ray spectrum of commercially available pigment anatase titanium oxide is shown in Figure 2. . The measurement conditions are the same as above except that the full scale is 4000 cps. Next, using this carrier, a catalyst for removing nitrogen oxides having tungsten oxide supported thereon was obtained in exactly the same manner as in Example 1. Example 4 The tungsten oxide supported catalyst obtained in Example 1 was
10g ammonium metavanadate and 25g oxalic acid
After impregnating with an aqueous solution of
It was dried for 12 hours and further calcined at 500°C for 3 hours to obtain a nitrogen oxide removal catalyst on which tungsten oxide and vanadium oxide were supported. Example 5 Vanadium oxide was supported on the tungsten oxide supported catalyst obtained in Example 2 in the same manner as in Example 4 to obtain a catalyst for removing nitrogen oxides. Example 6 Vanadium oxide was further supported on the tungsten oxide supported catalyst obtained in Example 3 in the same manner as in Example 4 to obtain a catalyst for removing nitrogen oxides. Comparative Example 1 A catalyst for removing nitrogen oxides on which tungsten oxide was supported was obtained in exactly the same manner as in Example 1, except that particulate silicic acid was not used. Comparative Example 2 In Example 1, titanium sulfate was thermally hydrolyzed to generate metatitanic acid without using particulate silicic acid, filtered, washed with water, dispersed in water again, and solized with barium chloride. The mixture was filtered and dried at 100°C for 12 hours, and then calcined at 500°C for 3 hours. This fired product was pulverized using a sample mill and the particle size was adjusted to obtain a powder carrier. Using this carrier, a catalyst for removing nitrogen oxides having tungsten oxide supported thereon was obtained in exactly the same manner as in Example 1. Comparative Example 3 Ammonium metavanadate 10 was added to the catalyst for nitrogen oxide removal supported on tungsten oxide obtained in Comparative Example 1.
After impregnating with an aqueous solution of g and 25 g of oxalic acid dissolved in water, it was dried at 100°C for 12 hours and further calcined at 500°C for 3 hours to support tungsten oxide and vanadium oxide for nitrogen oxide removal. I got a catalyst. Comparative Example 4 Vanadium oxide was supported on the tungsten oxide supported catalyst for removing nitrogen oxides obtained in Comparative Example 2 in exactly the same manner as in Comparative Example 3 to obtain a catalyst for removing nitrogen oxides. Each of the nitrogen oxide removal catalysts obtained in the above Examples and Comparative Examples contained 200 ppm of nitrogen oxides and ammonia.
200ppm, 10% water vapor, 12% carbon dioxide, 800ppm sulfur dioxide, and the balance nitrogen are brought into contact at a temperature of 380℃ and a space velocity of 5000hr ^-1 .
The nitrogen oxide (NOx) removal rate and sulfur dioxide (SO ₂ ) oxidation rate were measured. The results are shown in Table 1.
Note that the nitrogen oxide removal rate (%) and the sulfur dioxide oxidation rate (%) were determined by the following formulas. Nitrogen oxide removal rate (%) = (catalyst layer inlet NOx concentration - catalyst layer outlet NOx concentration) / (catalyst layer inlet NOx
concentration) x 100 Sulfur dioxide oxidation rate (%) = (catalyst layer inlet SO ₂ concentration - catalyst layer outlet SO ₂ concentration) / (catalyst layer inlet (SO ₂
+SO ₃ ) concentration) x 100

[Table] As is clear from the above results, the catalyst of the present invention has a higher nitrogen oxide removal rate than the catalyst of the comparative example, which uses a fired titanium oxide product prepared without using fine silicic acid as a carrier. is high, while the sulfur dioxide oxidation rate is low, which makes it possible to eliminate the disadvantages due to the formation of sulfur trioxide when removing nitrogen oxides in the gas mixture.

[Brief explanation of drawings]

Figure 1 shows the X-ray spectrum of the fired titanium oxide product used as a carrier in the method of the present invention, and Figure 2 shows the X-ray spectrum of titanium oxide as a pigment for comparison.
Shows the line spectrum.

Claims (1)

[Claims] 1. Fine particle silicic acid is added to titanium sulfate, thermally hydrolyzed, dried and fired, and the fired product thus obtained contains vanadium, tungsten, molybdenum,
A method for producing a catalyst for removing nitrogen oxides, which comprises supporting an oxide of at least one element selected from copper, iron, chromium, manganese, and cerium. 2. Adding fine particles of silicic acid to titanium sulfate, thermally hydrolyzing it, turning it into a sol, drying it, and firing it.The fired product thus obtained contains a mixture of vanadium, tungsten, molybdenum, copper, iron, chromium, manganese, and cerium. 2. The method for producing a catalyst for removing nitrogen oxides according to claim 1, wherein the catalyst supports an oxide of at least one element.