JPH0114808B2 - - 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 additives such as silica are added to titanium oxide and fired, the resulting fired product will generally have a larger surface area and improved heat resistance. According to the method, titanium oxide is formed by adding additives to titanium or titanium salts such as titanium sulfate, neutralizing and hydrolyzing the titanium salts, and calcining the titanium hydroxide thus formed. There is a problem in that titanium hydroxide tends to become orthotitanic acid, and therefore, when it is calcined, it tends to become rutile-type titanium oxide, which is unsuitable as a carrier or catalyst. On the other hand, it is already known that if metatitanic acid is calcined, anatase-type titanium oxide, which is a crystal form that is generally preferred as a carrier or catalyst, can be obtained, although there are other factors as well. However, according to the method of adding additives such as silica to metatitanic acid and baking it, it is difficult to obtain a mixture with a uniform composition. Because it is gel-like, additives cannot be uniformly dispersed in metatitanic acid.
Therefore, it is not possible to obtain a high-performance support or catalyst. Problems to be Solved by the Invention As a result of intensive research in order to solve the various problems described above, the present inventors have found that a tungsten compound and/or a molybdenum compound is used as an additive, and this is added to metatitanic acid in the form of a sol. By sintering in the presence of titanium, the crystal growth of titanium oxide is suppressed during sintering of metatitanic acid, and the crystal growth of titanium oxide remains in ungrown anatase-type crystals, resulting in a large surface area and improved heat resistance. It was discovered that it is possible to obtain a fired product with excellent mechanical strength, and by using the fired product as a carrier to support certain metal oxides, the synergistic effect of each oxide on the carrier and these metal oxides, The present invention was developed based on the discovery that it is possible to obtain a catalyst for removing nitrogen oxides that is unprecedentedly improved. Means for Solving the Problems The method for producing a catalyst for removing nitrogen oxides according to the present invention involves calcining sol-formed metatitanic acid containing at least one compound selected from a tungsten compound and a molybdenum compound; Products include vanadium, tungsten, molybdenum,
It is characterized by supporting an oxide of at least one element selected from copper, iron, chromium, manganese, and cerium. The tungsten compound used in the present invention is
Tungsten oxide is a precursor that forms tungsten oxide by firing, and examples of this precursor include ammonium metatungstate. Similarly, the molybdenum compound used in the present invention is molybdenum oxide and a precursor that gives molybdenum oxide through calcination, and examples of the precursor include ammonium molybdate. In the present invention, preferably, metatitanic acid is made into a sol, and at least one compound selected from the above-mentioned tungsten compound and molybdenum is added thereto, mixed, and fired. Alternatively, after adding at least one compound selected from the above tungsten compound and molybdenum to metatitanic acid, the metatitanic acid may be sol-formed and mixed. In any case, it is necessary to make the above-mentioned compound exist in metatitanic acid which is partially or completely solized, thereby allowing the above-mentioned compound to be uniformly mixed with metatitanic acid. The amount of the tungsten compound and/or molybdenum compound added is 5 to 50% based on titanium oxide.
When the amount added is less than 5% by weight, the effect of suppressing the crystal growth of metatitanic acid during firing is poor, while when it exceeds 50% by weight, the mixture with sol-formed metatitanic acid gelatinizes, making it difficult to mix uniformly, which is also undesirable because the above-mentioned effects are inferior. The method of solization is not particularly limited, and for example, metatitanic acid 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 it. Alternatively, if the sulfate roots are not removed by washing with water, add alkaline earth metal chlorides such as barium chloride, strontium chloride, calcium chloride, etc., or alkaline earth metal chlorides such as barium sulfate, strontium nitrate, calcium nitrate to metatitanic acid. Nitrate is added to fix the sulfate radicals as water-insoluble barium salts while the reaction mixture is partially or completely solified. 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. Note that metatitanic acid sol gels at a pH of 1 to 2 or higher, so it may be gelled if necessary, as long as the tungsten and/or molybdenum compound is sufficiently uniformly mixed therein. The mixture of metatitanic acid and the tungsten and/or molybdenum compound thus obtained is dried, then calcined at a temperature of 800°C or lower, preferably at a reaction temperature of 700 to 200°C, and pulverized.
Obtain a powdered baked product. In this case, according to the present invention, metatitanic acid is used, resulting in anatase-type titanium oxide, which is preferable as a carrier or catalyst in calcination. In addition, when the fired product is used as a carrier or catalyst in a predetermined shape such as a honeycomb shape, the dried product obtained by drying the above mixture can 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. Further, the powdered fired product described above can be molded into a desired shape and then fired again. In this case, after molding into the desired shape, the temperature is again below 800℃, preferably between 700℃ and 700℃.
It can be fired at a temperature of 200℃. In this way,
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 tungsten compounds and/or molybdenum compounds, the crystal growth of titanium oxide is suppressed during firing of metatitanic acid, and the ungrown anatase crystals remain, resulting in fired products with a large surface area and good heat resistance. It also 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 present invention contains at least one selected from tungsten compounds and molybdenum compounds and has excellent heat resistance, the reaction temperature may range from 200 to 600°C, but is preferably , in the range of 300-500℃. Also, the space velocity of gas is 1000 to 100000hr ^-1 ,
Preferably it is in the range of 3,000 to 300,000 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 nitrogen monoxide, as well as 200-2000 ppm nitrogen oxides.
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, a tungsten compound and a molybdenum compound are present in the sol-formed metatitanic acid, so that these compounds are present in the resulting mixture. evenly distributed,
Moreover, when this is fired, the titanium oxide remains in the ungrown anatase crystals due to the action of the above compounds, so the fired products obtained have a large surface area, excellent heat resistance, and mechanical resistance after molding. Strength is also significantly improved. The catalyst for removing nitrogen oxides according to the present invention uses such a calcined product as a carrier and supports metal oxides having catalytic activity for removing nitrogen oxides. Due to the synergistic effect with type titanium oxide, it 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 use. It is excellent as an industrial nitrogen oxide removal catalyst. 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. Reference Example 1 (Manufacture of fired products) Titanium sulfate solution obtained from the titanium oxide manufacturing process using the sulfuric acid method was thermally hydrolyzed to obtain metatitanic acid, 1 kg of this was taken as titanium oxide, and barium chloride (dihydrate) was added to it. 80g of the mixture was added to form a sol, and thoroughly stirred and mixed. Next, 250 ml of a 10% methylamine solution containing 110 g of ammonium paratungstate was added, thoroughly stirred and mixed, dried at 100°C for 12 hours, and further calcined at 500°C for 3 hours. This baked product is ground in a sample mill, the particle size is adjusted, an appropriate amount of water is added, kneaded, extruded into a lattice-shaped molded product using an extruder, heated from room temperature to 100°C to dry it, and then A fired product according to the present invention was obtained by firing at 500°C for 3 hours. The X-ray spectrum of the fired product thus obtained is shown in FIG. Since the peak is low and broad, it is clear that 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. Reference Example 2 (Manufacture of baked product) 1 kg of the same metatitanic acid as in Reference Example 1 was taken out in terms of titanium oxide, 80 g of barium chloride (dihydrate) was added thereto to form a sol, and the mixture was stirred and mixed for 1 minute. Next, 120g of ammonium molybdate
300 ml of a methylamine solution containing was added thereto, and the mixture was then fired in exactly the same manner as in Reference Example 1 to obtain a fired product. Example 1 An aqueous solution containing 10 g of ammonium metavanadate and 25 g of oxalic acid was added to the fired product obtained in Reference Example 1, thoroughly kneaded, and extruded into a lattice-shaped product using an extruder. The mixture was dried by heating to .degree. C., and then calcined at 500.degree. C. for 3 hours to obtain a catalyst for removing nitrogen oxides. Example 2 A catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Example 2, except that the fired product obtained in Reference Example 2 was used. Comparative Example 1 1 kg of the same metatitanic acid as in Reference Example 1 was taken out in terms of titanium oxide, and 80 g of barium chloride (dihydrate) was added to it to form a sol. After thorough stirring and mixing, it was dried at 100°C for 12 hours. Then, it was further baked at a temperature of 500°C for 3 hours. This fired product was pulverized using a sample mill to adjust the particle size. Next, 250 ml of a methylamine solution containing 110 g of ammonium paratungstate was added and kneaded, and an appropriate amount of water was added and kneaded, followed by extrusion molding into a lattice shape in exactly the same manner as in Reference Example 1, baking, and nitrogen gas. An oxide removal catalyst was obtained. Comparative Example 2 An aqueous solution of 10 g of ammonium metavanadate and 25 g of oxalic acid dissolved in water was added to the fired product obtained in Comparative Example 1, and an appropriate amount of water was added and kneaded, then extruded into a lattice shape and heated at 100°C. Dry for 12 hours,
The mixture was further calcined at 500°C for 3 hours to obtain a catalyst for removing nitrogen oxides. Comparative Example 3 A fired product was obtained in exactly the same manner as in Reference Example 1, except that metatitanic acid was not sol-formed with barium chloride. 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°C and a space velocity of 5000hr ^-1 .
The nitrogen oxide (NOx) removal rate and sulfur dioxide (SO ₂ ) oxidation rate were measured. Furthermore, since the fired products obtained in Reference Examples 1 and 2 themselves also had nitrogen oxide removal activity, the nitrogen oxide removal rate and sulfur dioxide oxidation rate were similarly 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, according to the catalyst of the present invention, the nitrogen oxide removal rate is high, but the sulfur dioxide oxidation rate is low, and when removing nitrogen oxides from the gas mixture, trioxide Disadvantages due to sulfur production can be eliminated.

[Brief explanation of drawings]

Figure 1 shows the X-ray spectrum of the fired titanium oxide product used in the method of the present invention, and Figure 2 shows the
The X-ray spectrum of pigment titanium oxide is shown for comparison.

Claims (1)

[Claims] 1. A solized metatitanic acid containing at least one compound selected from a tungsten compound and a molybdenum compound is 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.