JPH038820B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is directed to water-insoluble vanadyl sulfate (β-
VOSO ₄ ), barium sulfate, and a titanium compound. More specifically, the present invention aims at reducing sulfur coexisting in the exhaust gas when nitrogen oxides in the exhaust gas containing nitrogen oxides discharged from a fixed combustion device are reduced and purified in the presence of a reducing substance such as ammonia. A highly durable product for reducing and purifying nitrogen oxides that can prevent problems caused by oxides and dust, and can efficiently reduce and purify nitrogen oxides in exhaust gas at temperatures exceeding 380°C over a long period of time. This relates to a method for producing a catalyst. [Conventional technology] Nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are emitted from fixed combustion equipment in various factories, including boilers, power plants, and steel plants that use heavy oil and coal.
NOx in exhaust gas, which contains nitrogen oxides (NOx) such as sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), and dust, is expressed by the following formula: Many methods of reducing and purifying reducing substances such as ammonia in the presence of such substances and nitrogen oxide reduction and purification catalysts used in the process are already known. 4NO+NH ₃ +O ₂ →6H ₂ O+4N ₂ 6NO+4NH ₃ →5N ₂ +6H ₂ O 6HO ₂ +8NH ₃ →7N ₂ +12H ₂ O Typical nitrogen oxide purification catalysts include iron,
There are catalysts that use oxides such as copper and vanadium as catalyst components and support them on carriers such as alumina and titania. Among these catalysts, the V ₂ O ₅ -TiO ₂ catalyst has high NOx removal activity at low temperatures (around 300°C) and high SOx resistance, making it an excellent catalyst.
Since the activity of oxidizing SO ₂ to SO ₃ (SO ₂ oxidation activity) is large, a large amount of SO ₃ is generated on the catalyst, which combines with the added reducing substance ammonia and accumulates on the catalyst surface, or is heated. The drawback is that sulfur compounds such as acidic ammonium sulfate may accumulate in the exchanger or flue, causing various operational problems such as deterioration of the catalyst and corrosion of equipment. Furthermore, many nitrogen oxide purification catalysts using metal sulfates as carriers and/or catalyst components are already known. These catalysts are
Although the catalyst has relatively good SOx properties and long life, there are cases where an attempt is made to regenerate the catalyst by washing with water, or when the catalyst is contaminated by adhesion of dust in the exhaust gas, or when water comes into contact with the catalyst during operation. There are disadvantages in that the catalyst components may be eluted or the catalyst may disintegrate. For example, in the claims of JP-A-51-103869, there are descriptions of a large number of metal sulfate catalysts, but the catalyst described in this publication is on the third page, left column, 20th page. Row ~ Same page, right column, No. 6
As is clear from the description that there is no need to calcinate the catalyst during the preparation of the catalyst and that the catalyst components can be easily separated by washing with water, there is a major drawback in the water resistance of the catalyst, and it is difficult to regenerate the catalyst by washing with water. If you try to do so, the catalyst may collapse or the catalyst components may be eluted. Also, Japanese Patent Publication No. 57-30532, Japanese Patent Publication No. 59-35025
No. 1, etc., discloses a catalyst in which a titanium compound is treated with a silicon compound and fired to prepare a titanium and silicon-based carrier, and then a catalyst component such as vanadium is supported and fired again. The preparation method for these catalysts is complicated, and their long-term NOx removal activity may not be sufficient.
From an industrial standpoint, there is room for improvement. Japanese Patent Publication No. 56-32020 (West German Published Patent Publication No. 2842147) filed by the present applicant describes a catalyst comprising barium sulfate and vanadyl sulfate which is insoluble in water. The catalyst described in the publication is
It has excellent water resistance and SOx resistance, low activity to oxidize SO ₂ B to SO ₃ (SO ₂ oxidation activity), and high NOx removal activity at relatively low temperatures. Furthermore, JP-A No. 59-59249 discloses a solution of a vanadium compound in which the valence of vanadium is reduced to 4 by adding a reducing substance to a vanadium compound in which the valence of vanadium is 5 in the presence of water; A method for producing a catalyst for nitrogen oxide reduction and purification comprising a titanium compound, barium sulfate, and water-insoluble vanadyl sulfate, which comprises mixing sulfuric acid or an ammonium salt of sulfuric acid, barium sulfate, and titanium hydroxide, and then calcining the mixture. Are listed. The catalyst prepared by the method described in this publication has a NH ₃ NO (molar ratio) of 1 or less when exhaust gas is treated at 300 to 340°C.
It has the features of high NOx removal activity, little ammonia remaining in the exhaust gas after denitrification, and low SO ₂ oxidation activity. Said Japanese Patent Publication No. 56-32020, Japanese Patent Application Publication No. 59-59249
The catalyst containing water-insoluble vanadyl sulfate described in the above publication has the excellent features described above, but under high temperature conditions, for example when the exhaust gas temperature is
For long periods of time at high temperatures exceeding 380℃
There are drawbacks to NOx removal activity and SO ₂ oxidation activity, and there is room for further improvement in this respect. [Problems to be solved by the invention] Although the temperature of the exhaust gas to be treated varies depending on the type of combustion equipment and the installation position of the denitrification equipment, in recent years it has been It is often required to remove NOx from exhaust gas, which contains SOx, dust, etc. along with NOx. Among the conventionally known catalysts, there have been proposals for catalysts with low SO ₂ oxidation activity and high NOx removal activity, but as mentioned above, when applied to NOx removal under high temperature conditions, the NOx removal activity is low and the NOx removal activity is low. Or,
_SO2 oxidation activity is large and low. The present invention has low SO ₂ oxidation activity even when applied to the removal of NOx in high-temperature exhaust gas, and has excellent high-temperature characteristics that can stably maintain high NOx removal activity over a long period of time. The purpose of the present invention is to provide a method for producing a catalyst. [Means for Solving the Problems] The present inventors have discovered the water-insoluble vanadyl and As a result of further research, we were able to make full use of the features of catalysts made of barium sulfate, water-insoluble vanadyl sulfate, barium sulfate, and titanium compounds in the removal of NOx from high-temperature exhaust gas. We have arrived at the present invention. The present invention involves adding sulfuric acid or sulfuric acid to a solution of a vanadium compound in which the valence of vanadium is lower than 5 by reducing the valence of vanadium in the presence of a reducing substance and a solvent. A method for producing a catalyst for purification of nitrides consisting of water-insoluble vanadyl sulfate, barium sulfate, and titanium compounds by drying and calcining a slurry containing a mixture of ammonium salt, barium sulfate, and titanic acid. In terms of titanium, the content of aqueous sulfate radicals (SO ² ₄ ^- ) (SO ² ₄ ^- /TiO ₂ ) per 1 g of titanium dioxide ₍ TiO 2 ) is 50
The present invention relates to a method for producing a catalyst for purifying nitrogen oxides, which uses a titanic acid slurry of less than mg. In the present invention, the titanic acid slurry has an aqueous sulfuric acid radical (SO ² ₄ ^- ) content of 1 g of titanium dioxide (TiO 2 ) when the titanic acid in the slurry is converted to titanium dioxide (TiO ₂ ).
50 mg or less, preferably 30 mg or less, especially 10
mg or less of titanate slurry is used. Titanic acid usually has a large specific surface area of 100 to 300 m ² /g, and the average diameter of its primary particles is small, 30 to 50 Å, making it easy to aggregate. Therefore, it is necessary to uniformly disperse titanic acid to achieve the desired catalytic performance. For this purpose, titanic acid must be used as a titanate slurry, preferably an aqueous slurry. In addition, when the content of water-soluble sulfate groups is high, the water-soluble sulfate groups promote the aggregation of titanic acid, hinder the dispersion of titanic acid during catalyst preparation, and uniformly support the water-insoluble vanadyl sulfate, which is the active component of the catalyst. Therefore, it is necessary to thoroughly wash the titanate slurry with water as necessary and use a titanate slurry with a low content of water-soluble sulfate groups. When mixing titanate slurry, if you use a dried titanate slurry instead of titanate slurry or use one with a high content of water-soluble sulfate groups, the long-term NOx removal activity may decrease and the SO ₂ oxidation activity may increase. I don't like it because it makes me feel tired. Titanium acid slurry is mainly made of methane titanate, which is obtained by thoroughly washing titanium acid with water without drying it, which is obtained by neutralizing hydrolysis or thermal hydrolysis of titanium salts such as titanium tetrachloride and titanium sulfate. A titanic acid aqueous slurry as a component is preferable, and a titanic acid aqueous slurry produced by a sulfuric acid method is particularly preferable. It is preferable to use a titanic acid slurry with a concentration of 10 to 40% by weight, preferably 15 to 30% by weight in terms of titanium dioxide, as this will improve the dispersibility of titanic acid and the high humidity characteristics of the catalyst. . If the concentration is too high, the dispersibility of titanic acid tends to deteriorate, and if the concentration is too low, more heat is required for firing the catalyst. [Function] In the present invention, the mechanism by which a catalyst with low SO ₂ oxidation activity and high NOx removal activity even under high-temperature conditions is obtained has not been fully elucidated; Using less titanate slurry will improve the dispersion of titanate,
Sintering of thermally unstable titanic acid is suppressed by barium sulfate, which has a small specific surface area but is thermally stable, and the catalyst component, vanadyl sulfate, which is insoluble in water, is uniformly distributed between barium sulfate and titanic acid. This is thought to be due to the fact that titanic acid's large specific surface area and barium sulfate's thermal stability are fully utilized because they are dispersed and supported. The method for producing the catalyst of the present invention will be explained in detail. In the present invention, examples of the vanadium compound having a pentavalent vanadium include ammonium methanvanadate, metavanadate, vanadium pentoxide, and the like, with ammonium metavanadate being particularly preferred. Further, the reducing substance may be any substance that can reduce a pentavalent vanadium compound to a valence smaller than pentavalent (quadrivalent), such as organic carboxylic acids such as oxalic acid, citric acid, and tartaric acid. Of these, oxalic acid is preferred. In preparing a solution of a vanadium compound in which the valence of vanadium is reduced to a valence of less than 5 by reducing the valence of vanadium in the presence of a reducing substance and a solvent, For example, a pentavalent vanadium compound such as ammonium metavanadate is dissolved in a solvent such as water, and a reducing substance such as oxalic acid is added thereto.
Even if the method is carried out by reducing a vanadium compound of high valence, it is also possible to add
The reduction may also be carried out by adding a vanadium compound of vanadium. The solvent may be any solvent as long as it can dissolve the pentavalent vanadium compound and the reducing substance, but water is generally preferably used. In addition, the sulfuric acid or ammonium salt of sulfuric acid used in the present invention includes concentrated sulfuric acid, ammonium sulfate,
Examples include acidic ammonium sulfate, ammonium sulfite, ammonium persulfate, etc. Among them, ammonium sulfate is preferred because it is inexpensive and has good reproducibility of the intended catalyst. Sulfuric acid or an ammonium salt of sulfuric acid is necessary to form vanadyl sulfate, which is insoluble in water. ~2
Amounts such as gram atoms are preferred, and there is no advantage to using more than 2 gram atoms. Barium sulfate generally has a specific surface area of 10m ² /
Precipitated barium sulfate having an average particle diameter of 0.1 to 1.0 μm is preferably used. The order in which sulfuric acid or ammonium salt of sulfuric acid, barium sulfate, and titanate slurry are mixed into the solution of vanadium compound is not particularly limited, and it is sufficient to form a mixed slurry in which these are combined, and the order in which they are added is Either is fine. The important point at this stage is to use a titanic acid slurry with a small amount of water-soluble sulfate groups, as described above. The mixing ratio of the vanadium compound solution is 0.5 to 35% by weight, preferably 1 to 35% by weight in terms of vanadyl sulfate, which is insoluble in water.
10% by weight, barium sulfate 25 to 95% by weight, preferably 35 to 70% by weight, and titanate slurry 1 to 65% by weight in terms of titanium dioxide (TiO ₂ ), preferably 20% by weight.
It is appropriate to select the amount within the range of ~50% by weight. In addition, when mixing, acid clay,
Clay minerals such as activated clay and bentonite may be added and mixed in an amount of 5 to 30% by weight based on the finished catalyst. The pH of the mixed slurry obtained by mixing is between 2 and 2.
8, preferably 3 to 7. A part of the vanadium compound is adsorbed by barium sulfate and titanic acid through mixing, but the adsorption amount and adsorption state are estimated to be greatly affected by the pH of the slurry, and adjusting the pH of the slurry It is preferable that the PH of the slurry be within the above range because it becomes easier to obtain a catalyst with high NOx removal activity, low SO ₂ oxidation activity, and good high-temperature properties. The PH of the slurry can generally be adjusted within the above range without adding a PH regulator, but it is appropriate to adjust the PH using a suitable acid or alkali.
As the pH adjuster, it is preferable to use one that volatilizes during firing.As the acid, mineral acids such as hydrochloric acid and organic acids such as acetic acid can be used.As the alkali, ammonia,
Aqueous ammonia and amines such as ethanolamine and methylamine are suitable. The mixed slurry may be concentrated, shaped into a honeycomb shape, granules, etc., dried, and then fired, or dried, shaped, and fired. The desired catalyst can be obtained by drying and calcination. Generally, drying is suitably carried out in an air atmosphere at a temperature of 90 to 200°C to the extent that volatile components such as water are eliminated. Also, firing is performed at 200 to 500℃, preferably 350 to 450℃.
C., and the firing time is generally 1 to 24 hours, preferably 3 to 16 hours. The firing atmosphere is not particularly limited, and may be any atmosphere containing sulfur dioxide gas, ammonia, water vapor, nitrogen, oxygen, etc., but an oxygen-containing gas atmosphere such as air is economical and preferred. The vanadium compound used as a raw material by calcination is converted into water-insoluble vanadyl sulfate (β
-VOSO ₄ ), the catalyst contains almost no other vanadium compounds other than water-soluble vanadyl sulfate, but if it is in small amounts (approximately 5% by weight or less of the total vanadium compounds), other vanadium compounds may be present. There is no problem even if it contains vanadium compounds. According to the infrared absorption spectrum, vanadyl sulfate itself, ^{which is insoluble in water, is 940 -1} _cm
It has a characteristic absorption peak at 510 ^-1 cm and has a characteristic absorption peak at 510 -1 cm.
Sulfate]. If the concentration of vanadyl sulfate in the catalyst is 5% by weight or less, 940 ^-1
The infrared absorption spectra at cm and 510 ^-1 cm are not remarkable, but when analyzed using ESCA, vanadium has a valence of 4, and vanadium does not elute even when the catalyst is immersed in water. Recognized as insoluble vanadyl sulfate. Furthermore, although it is not clear from X-ray diffraction spectra what kind of titanium compound the titanic acid in the titanic acid slurry used as a raw material becomes in the catalyst, it turns out to be a complex titanium compound containing titanic acid and titanium dioxide. It is presumed that this is the case. [Example] In each example, the NOx removal activity (initial activity) was tested by filling a stainless steel reaction tube with 12 ml of catalyst crushed into 9 to 12 mesh, and
NO300ppm, _NH3 300ppm, SO2 _800ppm ,
A model gas consisting of 10% H ₂ O, 3% O ₂ and the remaining N ₂ (NH ₃ /NO = 1, molar ratio) was
It was flowed at a flow rate of 30000 hr ^-1 and maintained at 320°C, 350°C, 380°C and 410°C, and after 24 hours, the NOx content in the gas at the inlet and outlet of the reaction tube was measured using a chemiluminescent NOx analyzer. NOx (%) according to the following formula
I did it by the method of finding. NOx removal rate (%) ₌ X ₁ −X ₂ /X ₁ ×100 X ₁ = NOx concentration in the gas at the inlet of the reaction tube After measuring, a durability test was conducted at 380℃ for 2000 hours. In addition, to test the oxidation activity of SO ₂ , the model gas was flowed at a flow rate of 10,000 hr ^-1 in the same manner as described above, maintained at 350°C and 380°C, and after 72 hours, the gas at the inlet and outlet of the reaction tube was SO ₂ and
The SO ₃ concentration was analyzed and measured, and the SO ₂ oxidation rate (%) was calculated using the following formula. SO ₂ oxidation rate = Z / Y × 100 Y = ^SO ₂ concentration in the gas at the reaction tube inlet Z = SO ₃ concentration in the gas at the reaction tube outlet ^- ₄ ) The content (mg) is the amount per 1g of TiO ₂ (titanic acid converted to titanium dioxide), and the content was measured by fixing with barium. Example 1 An aqueous slurry of metatitanic acid produced by a thermal hydrolysis method of tan sulfate (an aqueous slurry of metatitanic acid produced by a sulfuric acid method) was washed with water to determine the content of water-soluble sulfate groups.
3.2 mg of metatitanic acid aqueous slurry (slurry concentration in terms of TiO ₂ 25% by weight) was prepared. Ammonium metavanadate 0.217 in water 6
Kg was added and heated to 70℃, and while stirring, oxalic acid (2
A solution of a vanadium compound is prepared by reducing vanadium by gradually adding 0.351 kg of aqueous salt, and to this solution, 0.368 kg of ammonium sulfate, 5.4 kg of precipitated barium sulfate powder, and the previously prepared metatitanic acid aqueous slurry are added with titanium dioxide. 4.4 kg in terms of conversion was added and mixed to obtain a mixed slurry with a pH of 3.5. The mixed slurry was heated to 100°C with stirring to form a paste, formed into a 4 mm diameter rod using an extruder, dried at 150°C in an air atmosphere for 5 hours, and then calcined at 450°C in an air atmosphere for 4 hours to form a catalyst. I got it. The resulting catalyst composition consisted of 2.0% by weight of water-insoluble vanadyl sulfate, 54.0% by weight of barium sulfate, and 44.0% by weight of a titanium compound (calculated as _TiO2 ),
The specific surface area of the catalyst was 73 m ² /g. The initial NOx removal rate and SO ₂ oxidation rate are shown in Table 1, and the long-term NOx removal rate is shown in Table 2. Example 2 The same procedure as Example 1 was carried out except that the amount of precipitated barium sulfate powder and metatitanic acid aqueous slurry used was changed, except that water-insoluble vanadyl sulfate 2.0% by weight and barium sulfate 70.0% were used. Weight% and titanium compound ( _TiO2 equivalent) 28.0% by weight
A catalyst consisting of The pH of the mixed slurry is
It was 3.1. The specific surface area of the catalyst was 42 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Example 3 In Example 1, the amount of precipitated barium sulfate powder and metatitanic acid aqueous slurry used was changed, and the paste before extrusion was acidified so that the acid clay in the catalyst was 15% by weight. Except for kneading the clay, the same procedure as in Example 1 was carried out to prepare water-insoluble vanadyl sulfate 2.0% by weight, barium sulfate 45.7% by weight, titanium compound 37.3% by weight and acidic clay.
A catalyst consisting of 15.0% by weight was produced. Note that the pH of the mixed slurry was 3.3. The specific surface area of the catalyst was 67 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Example 4 In the same manner as in Example 1, except that a metatitanic acid aqueous slurry having a water-soluble sulfate radical content of 29 mg (TiO ₂ equivalent slurry concentration 30% by weight) was used as the metatitanic acid aqueous slurry. A catalyst consisting of 2.0% by weight of insoluble vanadyl sulfate, 54.0% by weight of barium sulfate and 44.0% by weight of a titanium compound (calculated as TiO ₂ ) was produced. Note that the pH of the mixed slurry was 2.6. The specific surface area of the catalyst was 49 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Example 5 The same procedure as in Example 1 was carried out, except that a metatitanic acid aqueous slurry with a water-soluble sulfate radical content of 0.5 mg (slurry concentration 30% by weight in terms of TiO ₂ ) was used as the metatitanic acid aqueous slurry in Example 1. Water-insoluble vanadyl sulfate 2.0% by weight, barium sulfate 54.0% by weight and titanium compound (calculated as TiO ₂ ) 44.0% by weight
A catalyst consisting of The pH of the mixed slurry is
It was 3.8. The specific surface area of the catalyst is 68 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Example 6 Vanadyl sulfate, which is insoluble in water, was prepared in the same manner as in Example 1, except that the PH3.5 of the mixed slurry in Example 1 was changed to PH6.5 by dropping dilute ammonium water.
2.0% by weight of barium sulfate, 54.0% by weight of barium sulfate, and 44.0% by weight of titanium compound (calculated as TiO ₂ ). The specific surface area of the catalyst is 75 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Example 7 Water-insoluble vanadyl sulfate was prepared in the same manner as in Example 1, except that PH3.5 monoethanolamine of the mixed slurry was added dropwise to adjust the pH to 6.0.
2.0% by weight of barium sulfate, 54.0% by weight of barium sulfate, and 44.0% by weight of titanium compound (calculated as TiO ₂ ). The specific surface area of the catalyst was 74 m ² /g, and the catalyst performance test results are shown in Tables 1 and 2. Comparative Example 1 A catalyst consisting of 7.5% by weight of water-insoluble vanadyl sulfate and 92.5% by weight of barium sulfate was produced in the same manner as in Example 1, except that the metatitanic acid aqueous slurry was not used in Example 1. Note that the pH of the mixed slurry was 1.5. The specific surface area of the catalyst is 5 m ² /g, and the catalyst performance test results are shown in Tables 3 and 4. Comparative Example 2 A catalyst consisting of 2.0% by weight of water-insoluble vanadyl sulfate and 98.0% by weight of a titanium compound (calculated as TiO ₂ ) was prepared in the same manner as in Example 1, except that barium sulfate powder was not used in Example 1. Manufactured. Note that the pH of the mixed slurry was 3.4. The specific surface area of the catalyst was 89 m ² /g, and the catalyst performance test results are shown in Tables 3 and 4. Comparative Example 3 Example 3 was the same as in Example 1, except that titanic acid obtained by drying the same metatitanic acid slurry with a water-soluble sulfate radical content of 3.2 mg at 120°C for 6 hours in an air atmosphere was mixed instead of the metatitanic acid aqueous slurry. 1, 2.0% by weight of water-insoluble vanadyl sulfate, 54.0% by weight of barium sulfate, and a titanium compound (TiO ₂
A catalyst containing 44.0% by weight (converted) was produced. Note that the pH of the mixed slurry was 3.4. The specific surface area of the catalyst is 48 m ² /g, and the catalyst performance test results are shown in Tables 3 and 4. Comparative Example 4 The same procedure as in Example 1 was carried out, except that a metatitanic acid aqueous slurry having a water-soluble sulfate radical content of 68.5 mg (slurry concentration 30% by weight in terms of TiO ₂ ) was used instead of the metatitanic acid slurry in Example 1. A catalyst consisting of 2.0% by weight of water-insoluble vanadyl sulfate, 54.0% by weight of barium sulfate, and 44.0% by weight of a titanium compound (calculated as TiO ₂ ) was produced. Note that the pH of the mixed slurry was 2.2. The specific surface area of the catalyst was 43 m ² /g, and the catalyst performance test results are shown in Tables 3 and 4. Comparative Example 5 In Example 1, the vanadium compound solution was
Same as Example 1, except that ammonium sulfate and metatitanic acid aqueous slurry were mixed and dried at 120°C, then precipitated barium sulfate powder and a small amount of water were added to make a paste, and this was molded using an extruder. and 2.0% by weight of vanadyl sulfate, which is insoluble in water.
A catalyst consisting of 54.0% by weight of barium sulfate and 44.0% by weight of a titanium compound (calculated as TiO ₂ ) was produced. The specific surface area of the catalyst is 55 m ² /g, and the catalyst performance test results are shown in Tables 3 and 4.

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〔Effect of the invention〕

As is clear from the examples and comparative examples,
The catalyst obtained by the present invention can be used even at high temperatures.
It has the features of being able to maintain stable high NOx removal activity over a long period of time, low SO ₂ oxidation activity, and high exhaust gas treatment capacity per unit time. Further, according to the present invention, a durable catalyst can be obtained by firing only once, and there is an advantage that a particularly expensive catalyst raw material is not required. On the other hand, a catalyst containing no titanium compound produced without using titanate slurry (Comparative Example 1)
The NOx removal activity is stable even in the long term, but not only is the NOx removal activity low both initially and over the long term, but the SO ₂ oxidation activity is also large. In addition, a barium sulfate-free catalyst produced without using barium sulfate (Comparative Example 2) has high initial NOx removal activity and low SO ₂ oxidation activity, but the long-term
Poor NOx removal activity. Further, the catalyst manufactured using titanic acid powder instead of titanic acid slurry (Comparative Example 3) has low NOx removal activity over a long period of time. In addition, the catalyst using a titanate slurry with a high content of water-soluble sulfate groups (comparison row 4) has SO ₂
High oxidation activity. In addition, a catalyst manufactured by mixing titanate slurry with a vanadium compound solution, drying it, and then mixing barium sulfate (Comparative Example 5)
has low long-term NOx removal activity.

Claims (1)

[Claims] 1. A solution of a vanadium compound in which the valence of vanadium is reduced to a valence lower than 5 by reducing a vanadium compound whose valence is 5 in the presence of a reducing substance and a solvent, In a method for producing a nitrogen oxide purification catalyst consisting of water-insoluble vanadyl sulfate, barium sulfate and a titanium compound by drying and calcining a slurry in which sulfuric acid or an ammonium salt of sulfuric acid, barium sulfate and titanic acid are mixed, titanium As the acid, use a titanic acid slurry with a water-soluble sulfate radical (SO ² ₄ ^- ) content (SO ² ₄ ^- /TiO ₂ ) of 50 mg or less per 1 g of titanium dioxide (TiO 2 ) in terms of titanium dioxide _. A method for producing a nitrogen oxide purification catalyst characterized by: 2 The content of water-soluble sulfate radicals in the titanate slurry is
A method for producing a catalyst for purifying nitrogen oxides according to claim 1, wherein the amount is 30 mg or less. 3. The method for producing a nitrogen oxide purifying catalyst according to claim 1, wherein the slurry obtained by mixing sulfuric acid or an ammonium salt of sulfuric acid, barium sulfate, and titanic acid slurry with a solution of a vanadium compound has a pH of 2 to 8. 4. The method for producing a catalyst for nitrogen oxide purification according to claim 3, wherein the mixed slurry has a pH of 3 to 7. 5. The method for producing a catalyst for purifying nitrogen oxides according to claim 1, wherein the titanic acid concentration of the titanic acid slurry is 10 to 40% by weight in terms of titanium dioxide ( _TiO2 ). 6. The method for producing a catalyst for nitrogen oxide purification according to claim 1, wherein the titanic acid slurry is a titanic acid aqueous slurry produced by a sulfuric acid method.