JPS6242741A - Production of catalyst for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To obtain the titled nitrogen oxide removing catalyst having large surface area and excellent mechanical strength and heat resistance by adding fine-particle silica and a tungsten compd. and/or molybdenum compd. to colloidal orthotitanic acid and baking the mixture. CONSTITUTION:Orthotitanic acid is brought into sol and 5-50wt%, based on the titanium oxide, fine-particle silica and a tungsten compd. and/or a molybdenum compd. are added to the sol. Then the mixture is baked at <=800 deg.C. The tungsten compd. and the molybdenum compd. are the oxides or the precursors forming oxides on baking, the baked product is the titanium oxide of an ungrown anatase type crystal and is preferably used as the carrier of catalysts. Besides, a metallic oxide having catalytic activity on removing nitrogen oxides can be deposited on the baked product and those catalysts maintain high activity for a long period. Furthermore, the catalysts are practically and industrially excellent since the oxidation degree of sulfur dioxide is extremely low.

Description

Detailed Description of the Invention (Field of Sedentary Application) The present invention relates to a method for producing a catalyst for removing nitrogen oxides, and more particularly, to a method for producing the above-mentioned catalyst that does not oxidize sulfur dioxide during nitrogen oxide removal. .

(Prior Art) It is already known that titanium oxide calcined products are used as carriers or catalysts, but are there any important implications for carrier or catalyst functions? The surface area, crystal shape, mechanical strength, heat resistance, etc. to be given vary depending on the manufacturing method and the presence, type, amount, etc. of additives. Many manufacturing methods have been proposed in the past. For example, orthotitanic acid. Although there are other factors involved, it is already known that anatase-type titanium oxide can be obtained by calcining titanium oxide, which is a crystalline form that is generally preferred as a carrier or catalyst.

(Problems to be Solved by the Invention) However, according to the method of adding additives such as silica to orthotitanic acid and firing, it is difficult to obtain a mixture with a uniform composition. When adding to orthotitanic acid, since orthotitanic acid is in a gel form,
The additive cannot be uniformly dispersed in the orthotitanic acid, and therefore a high performance support or catalyst cannot be obtained.

The present invention solves all of these problems and proposes a method for producing a catalyst for removing nitrogen oxides that is unprecedented and excellent.

(A precautionary measure to solve the problem) As a result of intensive research on the above manufacturing method, the present inventors used a tungsten compound and/or a molybdenum compound as well as particulate silicic acid as additives, and turned them into a sol. By calcination in the presence of orthotitanic acid, the crystal growth of titanium oxide is suppressed during the calcination of orthotitanic acid, and the crystal growth of titanium oxide remains in the ungrown anatase type crystal. improved n
By using this product as it is, or by using it as a carrier and supporting a certain metal oxide, the synergistic effect of each oxide on the carrier and these metal oxides will result in a fired product. The present invention was based on the discovery that a catalyst for removing nitrogen oxides can be obtained with an improvement never seen before.

That is, the present invention provides at least one compound selected from (1) (a) fine-particle silicic acid, and (b) a tungsten compound and a molybdenized adduct.
Solized orthotitanium containing species compounds! It
: Manufacturing method of a catalyst for removing nitrogen oxides (2) (a) A sol-formed ortho-containing compound containing at least 181 compounds selected from 1+1 tungsten compounds and molybdenum compounds. The present invention relates to a method for producing a catalyst for removing nitrogen oxides, which comprises completely firing titanic acid and supporting an active component of the catalyst for removing nitrogen oxides on the fired product obtained.

The fine particle silicic acid used in the present invention is also known as white carbon, and has one characteristic of having 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.

Commercially available fine particle silicic acid that can be suitably used in the present invention includes, for example, the trade name Fine Seal (
(manufactured by Tokuyama Soda Co., Ltd.), Hisil, Vulcasil, Carplex (manufactured by J4 Nogi Pharmaceutical Co., Ltd.), Nip Seal, Toxil (manufactured by Tokuyama M R ■), Vita Seal, Siloid, Aerosil (manufactured by Nippon Aerosil Co., Ltd.), etc. You can learn all about it, but among these, especially those with an average particle size of 10 to 50 m
μ and a specific surface area of 200 to 300 m”/S′ are preferably used.

Further, the tungsten compound used in the present invention is tungsten oxide and a precursor that forms tungsten oxide by firing, and examples of this precursor include ammonium paratungstate.

Similarly, the molybdenum compound used in the present invention is molybdenum oxide and a precursor that gives molybdenum oxide by calcination, and examples of the precursor include ammonium molybdate.

In the present invention, the amount of fine particle silicic acid, tungsten compound, and/or molybdenum compound added is 5 to 50% by weight based on titanium oxide, and if it is less than 5% by weight, the amount of orthotitanic acid added is 5% to 50% by weight based on titanium oxide. The effect of suppressing the crystal growth during firing is poor, and the addition of these additives in the fired product has little effect on improving the performance of the catalyst or support for removing nitrogen oxides. Because the mixture with oxidized orthotitanic acid gels, it becomes difficult to mix uniformly, and the resulting fired product has a relatively low content of titanium oxide, which is then used for nitrogen oxide removal. When used as a catalyst or carrier, the performance of the catalyst and carrier based on titanium oxide is degraded, which is not preferred.

Further, in the present invention, the mixing ratio of the fine particle silicic acid and the tungsten compound and/or molybdenum compound is preferably 2 to 5 by weight of the fine particle silicic acid to 1 particulate silicic acid.

Based on this ratio, the content of silicic acid as a carrier-modifying effect is 1 to 25% by weight based on titanium oxide. If it is less than 1% by weight, the effect of adding silicic acid will be weakened, and if it is more than 25% by weight, it will lead to a decrease in strength and inhibition of activity, which is not preferable.

In the present invention, preferably, the entire orthotitanic acid is made into a sol, and after adding fine particles of silicic acid and at least one compound selected from the above-mentioned tungsten compounds and molybdenum compounds and mixing, the sol is fired. Alternatively, after adding fine particles of silicic acid and at least one compound selected from the above-mentioned tungsten compounds and molybdenum compounds to orthotitanic acid, the orthotitanic acid may be sol-formed and mixed. In any case, it is necessary to have the fine particles of silicic acid and all of the above compounds present in the orthotitanic acid that has been partially or completely solified, so that these additives can be uniformly mixed with the orthotitanic acid. There are no particular restrictions on the method of sol formation, for example, washing orthotitanic acid with water to remove most of all sulfate groups, and then washing with hydrochloric acid or nitric acid.
is added to make part or all of it into a sol. Or, especially by washing with water (ii! If the radish root is not removed, use barium chloride in orthotitanic acid), alkaline earth metal chlorides such as mum, strontium chloride, calcium chloride, or barium nitrate, strontium nitrate, nitric acid. A nitric acid group containing an alkaline earth metal such as calcium is added to fix the sulfate group as a water-insoluble barium salt, and the reaction mixture is partially or completely solified. The amount of these sol-forming agents added to the reaction mixture
It is selected appropriately depending on the degree of solization. still,
Since the orthotitanic acid sol gels at a pH of 1 to 2 or more, it may be gelled if necessary, as long as the tungsten compound and/or molybdenum compound is sufficiently uniformly mixed therewith.

The mixture of the orthotitanic acid thus obtained, the fine silica powder, and the tungsten compound and/or molybdenum compound is dried and then heated at a temperature of 800°C or less, preferably 700 to 200°C. Baked and crushed
In this case, a powdered baked product is obtained. In this case, according to the invention:
Since orthotitanic acid is used, it becomes anatase type titanium fluoride, which is preferable as a catalyst or carrier in baked gVC.

In addition, when the fired product is used as a catalyst or 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. 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 lower than 800°C, preferably 700-200°C.
It may be fired at a temperature of 00°C.

In this manner, according to the present invention, a fired titanium oxide product can be obtained in the form of a powder or a molded product.

In addition, in the present invention, in any of the above n cases,
If a powdered dried product or fired product is fully present with orthotitanic acid sol or gel, molded into the desired shape, and fired, various physical properties such as mechanical strength, porosity, specific surface area, and pore distribution can be improved. In addition, it is possible to completely reduce shrinkage during firing by ``4''. In such a case, the appropriate amount of orthotitanic acid sol or gel added is 5 to 50% by weight of the weight of the molded product in terms of titanium oxide. .

Of course, during molding, conventionally known molding aids for AN, such as Avicel and methyl cellulose, may also be used.

In the present invention, the firing atmosphere is not limited at all, and may be air, combustion gas, inert gas, or the like.

As described above, the fired titanium oxide product obtained according to the present invention is not limited by any theory, but due to the presence of fine particles of silicic acid and a tungsten compound and/or a molybdenum compound, the titanium oxide fired product is made of orthotitanic acid. Since the crystal growth of titanium oxide is suppressed during firing and remains as an ungrown anatase crystal, the resulting fired product has a large surface area, excellent mechanical strength and heat resistance, and can be used as a catalyst as it is. It can be suitably used as a catalyst carrier or as a catalyst carrier.

The fact that the calcined product obtained according to the present invention remains ungrown anatase is shown by the fact that its X-ray spectrum has low and broad peaks, as shown in Figure 1. In the case of anatase titanium oxide for pigments, its complete X-ray spectrum is as shown in Figure 2.
Because the crystals have grown extremely well, the peak is high and sharp.

When using the fired titanium oxide product obtained as described above as a carrier, if the pressed body is supported on an oxide that is known to have catalytic activity for removing dinitrogen dispersions, the fired product can be fired. Due to the unexpected synergistic effect with the gold-containing oxide, it is possible to obtain a catalyst for removing nitrogen oxides with excellent selective catalytic reduction activity of nitrogen x oxides using ammonia as a reducing agent.

In the present invention, at least one catalyst active component for nitrogen oxide removal is selected from vanadium, tungsten, molybdenum, copper, iron, chromium, manganese, and cerium.
Support oxides of certain elements. The method for supporting the above-mentioned oxide on the fired titanium oxide product can be any method conventionally used for the preparation of catalysts. After being completely impregnated with or coated with a solution or dispersion containing , it may be fired to a predetermined temperature as necessary. Maku,
Of course, the powdered fired product is kneaded with the solution or dispersion, molded into a desired shape, and then 7'? After that, the catalyst 1 for removing nitrogen oxides of the present invention can also be obtained by calcining at a predetermined temperature as necessary.

In order to remove nitrogen oxides from a hot gas containing nitrogen oxides using the catalyst of the present invention, α is 5 to 5 times the mole of nitrogen oxides contained in the mixed gas, and α is 1 to 2 times the mole of nitrogen oxides contained in the mixed gas. Ammonia is added and passed through the reaction bed completely filled with the catalyst. Any of a moving bed, a fluidized bed, a fixed bed, etc. can be used as the reaction bed. The catalyst of the present invention contains fine particles of silicic acid and has excellent heat resistance.The reaction temperature may range from 200 to 600°C, but is preferably from 500 to 500°C. Also, the space velocity of the gas is 1. [100-10
0. OOOhr-', preferably Ao 00-5 Q
, 000hr-1.

The catalyst according to the invention can be used for the treatment of any gas containing nitrogen oxides, in particular boiler exhaust gases, i.e. 100-1000 ppm nitrogen oxides, mainly nitrogen monoxide, as well as 200-2000 ppm. sulfur oxides, mainly sulfur dioxide, 1 to 10 volume t% oxygen,
It can be suitably used to remove nitrogen oxides and gold from exhaust gas containing 5 to 20 volumes of carbon dioxide gas and 5 to 20 volumes of water vapor.

(Function) As described above, in the method of the present invention, fine particle silicic acid and at least one metal selected from a tungsten compound and a molybdenum compound are present in the sol-formed nine-orthotitanic acid. The compound is uniformly dispersed, and when it is completely fired, the titanium oxide remains as an ungrown anatase crystal due to the action of the compound, so the fired product has a large surface area and is easy to use with the machine. The mechanical strength and heat resistance are significantly improved. Therefore, a catalyst for removing nitrogen oxides consisting of such a fired product itself, or a catalyst with a catalytic activity of 1 for removing nitrogen oxides.
! - In the catalyst for removing nitrogen oxides obtained by fully supporting metal dispersions, the growth of anatase-type titanium oxide, particulate silicic acid, tungsten oxide and
Due to the synergistic action with molybdenum oxide or molybdenum oxide, or the synergistic action between these and the above metal oxides, it not only maintains high nitrogen oxide removal activity for a long period of time even under severe usage conditions, but also has a high nitrogen oxide removing activity. Since the oxidation rate to sulfur oxide is extremely low, it is suitable as a practical and industrial catalyst for removing nitrogen oxides.

(Examples) The present invention will be fully explained below with reference to Examples, but the present invention is not limited in any way by these Examples.

Example 1 A titanium sulfate solution obtained from the titanium oxide production process using the sulfuric acid method was neutralized and hydrolyzed with aqueous ammonia to obtain orthotitanic acid, which was extracted as nt-titanium oxide and then barium chloride hydrated. 80 ff was added to form a sol, and thoroughly stirred and mixed. Next, fine particle silicic acid Fine Seal (manufactured by Tokuyama Soda Co., Ltd.) 2009 and 10-thimethyl-7mine solution 250I7! containing all ammonium paratungstate 110f! / all added, thoroughly stirred and mixed, dried at 100°C for 12 hours, and further calcined at 500°C for 3 hours. All samples of this fired product were ground using a mill to adjust the particle size. Add an appropriate amount of water to this mixture, knead it, extrude it into a lattice-shaped molded product using an extruder, heat it from room temperature to 100°C to dry it, and then bake it at 500°C for 3 hours to obtain a baked product. I got it. This calcined product should be used in its entirety as a catalyst for removing nitrogen oxides.

The entire X-ray spectrum of the fired product thus obtained is
As shown in the figure. Since the peak is low and wide, it is clear that the anatase crystal remains ungrown.

The X-ray spectrum was obtained using an X-ray diffractometer R manufactured by Rigaku Denki Co., Ltd.
The measurement was performed using AD-It At, and the measurement conditions were as follows.

Scanning speed tail 1°/4 minutes full scale 1000 cps time constant
1 second chart speed 101111/min targetha
Copper tube voltage 50 Kv Tube current 101! IA For comparison, the complete X-ray spectrum of the 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.

Example 2 A baked product was prepared in the same manner as in Example 1, except that in place of ammonium paratungstate, 500 ml of methylamine solution containing 120 ff of ammonium molybdate was used. This was used as it was as a catalyst for removing nitrogen oxides.

Example 3 One part of the powdered calcined product obtained in Example 1 was mixed with 250mj of a 10% methylamine solution containing 1102m of ammonium paratungstate and 10f of ammonium metavanadate.
After adding i and kneading, it was extruded into a lattice-shaped molded product using an extruder, dried by heating from room temperature to 100°C, and then fired at 500°C for 3 hours to completely support tungsten oxide and vanadium oxide. All catalysts for removing nitrogen oxides were used.

Example 4 The powdered calcined product obtained in Example 2 was treated in the same manner as in Example 3, and a nitrogen oxide removal catalyst fully supported on tungsten oxide and vanadium oxide was prepared. To the obtained powdered fired product 1g, aroused manganese e
57! A fired lattice-shaped product was obtained in exactly the same manner as in Example 1, except that the amount of lattice-shaped molded product was loaded.

this? fffffl wire compound removal catalyst was used.

Example 6 A fired lattice shaped product was obtained in exactly the same manner as in Example 2 except that 5% by weight of manganese oxide was completely supported on the powdered fired product 11C4j obtained in Example 2.

Comparative Example 1 A fired product was obtained in exactly the same manner as in Example 1, except that orthotitanic acid was not sol-formed using barium chloride. This whole product was used as it was as a catalyst for removing nitrogen oxides.

Comparative Example 2 In Example I, no solization of orthotitanic acid with barium chloride was carried out, and in place of ammonium paratungstate in Example 1, 300 d of methylamine solution containing 120 ff of ammonium molybdate was used.
A baked product 1 was obtained in the same manner as in Example 1 except that t-9 was used.

This was used as it was as a catalyst for removing nitrogen oxides.

Comparative Example 5 Ikg of the fired product obtained in Comparative Example 1 was thoroughly mixed with an aqueous solution containing 101F of ammonium metavanadate and 259 oxalic acid, extruded, and then heated at 100°C for 2 hours.
After drying for time W, it was calcined at 500°C for 6 hours to obtain a catalyst for removing nitrogen oxides.90 Comparative Example 4 1 kg of the calcined product obtained in Comparative Example 2 contained 10 f of ammonium metavanadate and 25 ft of oxalic acid. Add an aqueous solution of
After drying for an hour, it was calcined at 500° C. for 3 hours to obtain a catalyst for removing nitrogen oxides.

Comparative Example 5 Same as Example 1, IK as orthotitanic acid total titanium oxide
9 Take out, add 80fi of barium chloride (dihydrate), make a sol, stir thoroughly, mix well, and heat at 100℃ for 12 hours.
It was dried for an hour and then fired at 500°C for 3 hours. All of this is crushed and the particle size is adjusted. To this were added 200F fine-particle silicic acid Fine Seal (manufactured by Tokuyamaso-j! Co., Ltd.) and 250tjQ of a 10-thimethylamine solution containing 110f'i of ammonium paratungstate, stirred and mixed thoroughly, and then added an appropriate amount of water. , kneaded, extruded into a lattice-shaped molded product using an extruder, heated from room temperature to 100°C and dried,
Next, it was calcined at 500° C. for 5 hours to obtain a catalyst for removing nitrogen oxides.

Comparative Example 6 A catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Comparative Example 3, except that the fired titanium oxide product obtained in Comparative Example 5 was used.

Comparative Example 7 A catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Comparative Example 5, except that the fired product obtained in Comparative Example 1 supported a total of 5% by weight of manganese oxide.

Comparative Example 8 A catalyst for removing nitrogen oxides was obtained in exactly the same manner as in Comparative Example 3, except that the fired product obtained in Comparative Example 2 supported 5% by weight of manganese oxide.

Each of the nitrogen oxide removal catalysts obtained in the above examples and comparative examples contained 200 ppm of nitrogen oxides and 200 p of ammonia.
pm, water vapor 10 cm, carbon dioxide 12 cm, sulfur dioxide 800 ppm, balance i * 77 was brought into contact at a temperature of 580°C and a space velocity of 5000 hr to remove nitrogen oxides (NO). rate and sulfur dioxide (S0
2) Oxidation i' was measured. The results are shown in Table 2. In addition, nitrogen oxide removal rate (%) and sulfur dioxide oxidation rate (%) F
f, each calculated using an n-th equation.

Nitrogen oxide removal rate (CH) = (Catalyst debris inlet Hox concentration - catalyst layer outlet NOx 9)/' (catalyst layer inlet NOx concentration)
100 Sulfur dioxide oxidation ME (%) = (Catalyst layer population SO
2 concentration - catalyst layer outlet so2 concentration)/(catalyst layer inlet (So2 concentration)
, +80. ) Concentration) Disadvantages due to the formation of sulfur trioxide during dispersion removal can be eliminated.

[Brief explanation of the drawing]

FIG. 1 shows an X-ray spectrum of a fired titanium oxide product obtained by the method of the present invention, and FIG. 2 shows an X-ray spectrum of a titanium oxide pigment for comparison. Sub-agent 1) Meifuku agent Ryo Hagi − Sub-agent ′t Atsuo Nishi Figure 1 2θ

Claims (2)

[Claims] (1) A nitrogen oxide removal catalyst characterized by firing a sol-formed orthotitanic acid containing (a) fine particle silicic acid and (b) at least one compound selected from a tungsten compound and a molybdenum compound. manufacturing method. (2) Calculating a sol-formed orthotitanic acid containing at least one compound selected from (a) fine-particle silicic acid and (b) a tungsten compound and a molybdenum compound;
A method for producing a catalyst for removing nitrogen oxides, which comprises making the obtained fired product support an active component of the catalyst for removing nitrogen oxides.