JP2022159206A - Denitration catalyst - Google Patents

Abstract

To provide a denitration catalyst having high activity.SOLUTION: A denitration catalyst contains a complex oxide of vanadium and molybdenum. The complex oxide is a mixed valence compound containing trivalent, tetravalent and pentavalent vanadium. The vanadium contained in the complex oxide has a number of cations of 0.7 or more. The complex oxide binds to the surface of a titanium oxide.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a denitration catalyst capable of purifying nitrogen oxides in exhaust gas.

Conventionally, as a denitration catalyst that removes nitrogen oxides (NO _x ) in exhaust gas by selective reduction with a reducing agent such as ammonia, a honeycomb-shaped catalyst in which active ingredients such as tungsten oxide and vanadium oxide are supported on a titanium oxide carrier. Molded products are used industrially (Patent Document 1). In recent years, it is also used as a catalyst for removing nitrogen oxides in the exhaust gas of boilers, garbage incinerators, etc., and from the viewpoint of suppressing the generation of dioxins, it is desired to operate at a temperature of about 200° C. or less. As denitration catalysts to solve this problem, the denitration catalysts of Patent Documents 2 and 3 have been proposed, and the demand for highly active denitration catalysts, especially at low temperatures, is increasing.

JP 2004-81995 A JP-A-11-165068 Japanese Patent Publication No. 2007-520327

An object of the present invention is to provide a denitration catalyst with high activity.

The present invention includes a composite oxide of vanadium and molybdenum, wherein the composite oxide is a mixed-valence compound containing trivalent, tetravalent and pentavalent vanadium, and the number of vanadium cations contained in the composite oxide is is 0.7 or more, and the composite oxide is bonded to the surface of the titanium oxide.

Since the denitration catalyst of the present invention has high NO _x selective reduction activity, it can efficiently remove NO _x not only in a high temperature range but also in a low temperature range of about 200° C. or lower.

1 is an X-ray photoelectron spectroscopy (XPS) spectrum of the denitration catalyst obtained in Example 1. FIG. 4 is a scanning electron microscope (SEM) image of the denitration catalyst obtained in Example 2. FIG.

Embodiments of the present invention are described in further detail below.

[Denitration catalyst of the present invention]
The denitration catalyst of the present invention contains a composite oxide of vanadium and molybdenum, the composite oxide is a mixed-valence compound containing trivalent, tetravalent and pentavalent vanadium, and the vanadium contained in the composite oxide is The number of cations is 0.7 or more, and the composite oxide is bonded to the surface of the titanium oxide. The present invention provides a denitration catalyst with enhanced _NOx selective reduction activity by controlling the number of vanadium cations within a certain range.

Complex oxides of vanadium and molybdenum are mixed valence compounds containing trivalent, tetravalent and pentavalent vanadium. The valence of vanadium in this composite oxide is affected by the valence of molybdenum contained in the composite oxide and the state of bonding to the surface of the titanium oxide. The valence state of vanadium can be defined by the number of cations, and by setting the number of cations to 0.7 or more, the _NOx selective reduction activity increases. This is the result of controlling the valence of molybdenum and the bonding state with titanium oxide, and controlling the valence of vanadium in the composite oxide so as to obtain the optimum band structure for selective reduction activity of _NOx . Furthermore, in the denitration catalyst of the present invention, since vanadium with different valences is dispersed in the composite oxide, the dispersibility of vanadium is higher than that of conventional denitration catalysts simply containing vanadium oxides with different valences. . Therefore, the denitration catalyst of the present invention has higher _NOx selective reduction activity than conventional denitration catalysts.

The vanadium cation number contained in the vanadium and molybdenum composite oxide is preferably in the range of 0.7 or more and 2 or less, more preferably in the range of 0.9 or more and 1.5 or less, and 1 or more and 1 .4 or less is particularly preferred. When the number of cations of vanadium is within this range, the _NOx selective reduction activity is further improved.

A composite oxide of vanadium and molybdenum is bonded to the surface of the titanium oxide. This is different from a composite oxide in which vanadium, molybdenum, and titanium are mixed in the same crystal structure, and the composite oxide of vanadium and molybdenum is bound to the surface of titanium oxide via oxygen. ing. This clearly distinguishes between the complex oxide phase and the titanium oxide phase.

The titanium oxide is preferably titanium dioxide, and more preferably has an anatase crystal structure. When such a titanium oxide is used, NO _x selective reduction activity tends to be high. In addition, the crystallite diameter of the titanium oxide having an anatase crystal structure is preferably in the range of 5 nm or more and 40 nm or less, which is obtained from the half-value width of the diffraction peak of the (101) plane. It is more preferably in the range of 10 nm or less. When the crystallite size of the titanium oxide, which is an anatase-type crystal, is within this range, it becomes easier to bond with the composite oxide containing vanadium and molybdenum. The content of titanium oxide is preferably 60% by mass or more, more preferably 65% by mass or more, and particularly preferably 70% by mass or more in terms of TiO ₂ .

Conventionally, denitration catalysts with a large specific surface area are known to have good _NOx selective reduction activity. In contrast, the denitration catalyst of the present invention exhibits good _NOx selective reduction activity even if the specific surface area is small. Specifically, even if it is less than 100 m ² /g or in the range of 50 m ² /g or more and 95 m ² /g or less, it exhibits good NO _x selective reduction activity.

The denitration catalyst of the present invention may contain components other than the composite oxide of vanadium and molybdenum. For example, it may contain vanadium oxide and molybdenum oxide. The content of vanadium (converted to V ₂ O ₅ ) is preferably in the range of 1% by mass or more and 20% by mass or less, including the vanadium contained in the composite oxide, and in the range of 5% by mass or more and 15% by mass or less. More preferably, it is in the range of 6% by mass or more and 10% by mass or less. In addition, the content of molybdenum (in terms of _MoO3 ), including the molybdenum contained in the composite oxide, is preferably in the range of 0.5% by mass to 15% by mass, and 1% by mass to 10% by mass. is more preferably in the range of 2% by mass or more and 8% by mass or less is particularly preferable. When the contents of vanadium and molybdenum are within this range, the _NOx selective reduction activity tends to be high. In addition, metal components such as tungsten, chromium, manganese, iron, nickel, copper, silver, gold, palladium, yttrium, cerium, neodymium, indium, iridium, and antimony may be included as components other than vanadium and molybdenum. . These act as co-catalysts and affect catalyst performance, and their content (in terms of metal) is preferably 3% by mass or less.

The denitration catalyst of the present invention preferably contains sulfur. The sulfur content (in terms of SO ₄ ) is preferably in the range of 0.1% by mass or more and 5% by mass or less, more preferably in the range of 0.5% by mass or more and 4% by mass or less. It is particularly preferable to be in the range of 5% by mass or more and 3% by mass or less. Sulfur contained in the denitration catalyst of the present invention affects the band structure of vanadium and has a positive effect on NO _x selective reduction activity.

In addition to these components, inorganic components such as glass fiber, silica, and alumina may be included as reinforcing materials. These components work to improve the moldability of the denitration catalyst and maintain its strength.

The shape of the denitration catalyst of the present invention may be a conventionally known shape such as pellets or honeycomb, preferably honeycomb. Specifically, the outer diameter of the honeycomb is preferably in the range of 30 mm or more and 300 mm or less, more preferably in the range of 50 mm or more and 200 mm or less. The length of the honeycomb is preferably in the range of 100 mm or more and 3000 mm or less, more preferably in the range of 300 mm or more and 1500 mm or less. The through-holes (hereinafter sometimes referred to as cell pitch) of the honeycomb are preferably in the range of 1 mm or more and 15 mm or less, and more preferably in the range of 2 mm or more and 10 mm or less. The partition wall thickness of the honeycomb is preferably in the range of 0.1 mm or more and 2 mm or less, and more preferably in the range of 0.1 mm or more and 1.5 mm or less. The open area ratio of the honeycomb is preferably in the range of 60% or more and 85% or less, more preferably in the range of 70% or more and 85% or less. When the shape of the honeycomb falls within this range, the NO _x selective reduction activity per unit volume tends to increase while maintaining the strength of the honeycomb structure.

The denitrification catalyst of the present invention can be used _by adding a reducing agent such as ammonia to exhaust gas containing NOx, especially exhaust gas containing _NOx or _SOx , such as exhaust gas from a boiler or a waste incinerator, and containing heavy metals or dust. It is suitably used for the _NOx removal method in which catalytic reduction is carried out by Further, it can be used at the reaction temperature of a conventionally known denitration catalyst, for example, the reaction temperature can be 150° C. or more and 400° C. or less. In particular, the denitration catalyst of the present invention exhibits high activity in the temperature range of 170°C or higher and 270°C or lower, and particularly exhibits good _NOx selective reduction activity in the temperature range of 170°C or higher and 200°C or lower.

[Method for producing the denitration catalyst of the present invention]
A method for producing the denitration catalyst of the present invention will be described below.

The denitration catalyst of the present invention can be prepared, for example, using a production method comprising the following steps.
1) A mother liquor preparation step of mixing water, sulfuric acid, a vanadium raw material, a molybdenum raw material and a complexing agent to prepare a mother liquor 2) A mixing step of mixing titanium oxide and the mother liquor to prepare a mixture 3) The mixture and precipitation 4) a reaction step of preparing a molding clay in which a coprecipitate of vanadium and molybdenum is bonded to the titanium oxide by mixing with an agent; A calcining step of calcining the compact to prepare a denitration catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of the titanium oxide.

Each step will be described in detail below.

In the mother liquor preparation step, a vanadium raw material, a molybdenum raw material, a complexing agent and sulfuric acid are dissolved in water to prepare a mother liquor. Here, vanadium and molybdenum are raw materials for making composite oxides. The complexing agent coordinates to vanadium or molybdenum ions to form a complex. Sulfuric acid is for coordinating with titanium oxide. The mother liquor can be prepared by dissolving these raw materials in water.

It is preferable to use soluble salts as raw materials of vanadium and molybdenum. For example, vanadate, vanadium sulfate, or vanadium chloride is preferably used as the vanadium raw material, and ammonium metavanadate is particularly preferably used. Alternatively, the vanadium oxide may be dissolved with an acid. As the molybdenum raw material, molybdate, molybdenum sulfate, molybdenum chloride, or the like is preferably used, and ammonium molybdate is particularly preferably used. Alternatively, the molybdenum oxide may be dissolved with an acid. Moreover, these may be used individually by 1 type, and may use 2 or more types together. Also, the amounts of the raw materials of vanadium and molybdenum to be added are appropriately adjusted according to the composition of the finally obtained denitration catalyst.

The complexing agent is preferably a compound having an amine and a hydroxy group, more preferably an alkanolamine, and particularly preferably ethanolamine. These complexing agents coordinate with vanadium ions or molybdenum ions in the mother liquor to form complexes and stabilize them. In addition, it also works to exchange ligands with sulfuric acid coordinated to titanium oxide in the process described later. Therefore, the complexing agent is preferably added after dissolving the vanadium and molybdenum raw materials in water. At this time, the amount of the complexing agent added is preferably in the range of 0.1 mol or more and 6 mol or less, and in the range of 0.5 mol or more and 3 mol or less with respect to the molar amount of vanadium and molybdenum. is more preferred. Thus, vanadium and molybdenum ions are stabilized by adding the required amount of complexing agent to form the complex.

Sulfuric acid is coordinated to the surface of the titanium oxide added in the process described later, and the vanadium and molybdenum are immobilized on the surface of the titanium oxide by a ligand exchange reaction with the vanadium and molybdenum complexes. Added. Therefore, the amount of sulfuric acid added is preferably in the range of 0.001 mol or more and 0.1 mol or less, more preferably in the range of 0.01 mol or more and 0.05 mol or less, relative to the molar amount of titanium. more preferred. Since the purpose is to coordinate to the surface of the titanium oxide, the amount of sulfuric acid to be added may be small relative to the molar amount of titanium.

Other soluble components may be added in this mother liquor preparation step. For example, a raw material containing the above-mentioned co-catalyst component may be dissolved.

In the mixing step, the mother liquor prepared in the mother liquor preparation step and the titanium oxide are mixed to prepare a mixture. Here, sulfuric acid contained in the mother liquor is coordinated to the surface of the titanium oxide. The titanium oxide is preferably titanium dioxide, and more preferably has an anatase crystal structure. When such a titanium oxide is used, NO _x selective reduction activity tends to be high. In addition, the crystallite diameter of the titanium oxide having an anatase crystal structure is preferably in the range of 10 nm or more and 40 nm or less, which is obtained from the half-value width of the diffraction peak of the (101) plane, 5 nm or more, It is more preferably in the range of 10 nm or less. When the crystallite size of titanium oxide having an anatase-type crystal structure is within this range, it becomes easier to bond with a composite oxide containing vanadium and molybdenum. The amount of titanium oxide to be added is appropriately adjusted according to the composition of the finally obtained denitration catalyst.

A conventionally known method can be used for the mixing method. For example, a kneader, high speed mixer, ball mill, or the like can be used. These methods are appropriately selected depending on the amounts of mother liquor and titanium oxide. If the material becomes clay and puts a load on the apparatus, it is preferable to use a kneader or a high-speed mixer.

In the reaction step, the mixture is mixed with a precipitant to prepare a molding clay having a co-precipitate of vanadium and molybdenum bonded to the surface of the titanium oxide. In this step, the mother liquor components contained in the mixture are neutralized to form a coprecipitate of vanadium and molybdenum. At this time, the complexing agent is coordinated on the surface of the coprecipitate, and by ligand exchange with sulfuric acid coordinated on the surface of the titanium oxide, the coprecipitate and the surface of the titanium oxide A bond occurs.

A conventionally known precipitant can be used. For example, precipitants such as sodium carbonate, soda ash, and aqueous ammonia can be used. The amount of the precipitant added is appropriately adjusted so that the pH of the mother liquor contained in the mixture is in the range of 6 or more and 9 or less. If the mixture is clay-like and pH measurement is difficult, the amount of precipitant required for neutralizing the mother liquor can be experimentally confirmed in advance, and the amount added can be adjusted. If the mixture is not clay-like, it is adjusted to a molding clay suitable for molding by adjusting the water content, adding a binder, and the like.

In the molding step, the molding clay is molded to prepare a molding. It can be molded into a conventionally known shape such as pellets or honeycombs. For use as a denitration catalyst, it is preferable to form a honeycomb. As for the molding method, conventionally known methods can be used, and for example, pellets or honeycombs can be molded using an extruder. The molded body may be dried by a conventionally known method so as not to cause cracks or the like.

In the firing step, the compact is fired to prepare a denitration catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of titanium oxide. A conventionally known method can be used for the firing method. For example, a method of firing in air using a heating furnace such as an electric furnace and a gas furnace can be used. The firing temperature is preferably 300° C. or higher and 500° C. or lower. The sintering time depends on the sintering temperature, but may generally be in the range of 1 hour or more and 48 hours or less.

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below. It should be noted that the present invention is not limited to the contents of the examples.

[Measuring method]
Each measurement method employed in the present application is described below.
[1] Composition The denitration catalysts obtained in the examples were pulverized to prepare samples for evaluation. A solution was prepared by dissolving this with an acid, and the composition of various components was calculated by high frequency inductively coupled plasma emission spectrometry (apparatus name: ICPS-8100).
[2] Valence of vanadium The reaction surfaces of the denitration catalysts obtained in the examples (the outer surface of the pellets, the outer surface of the partition walls of the honeycomb) were cut into pieces so that they could be measured, and evaluated. A sample was prepared for This was set on a sample stand and subjected to X-ray photoelectron spectroscopy (XPS) under the following conditions. The spectrum obtained from this measurement was analyzed, and if peaks were detected in the ranges below, it was determined that these valences of vanadium were contained.
V5+: ^517.20 eV±0.2 eV
V4 ⁺ : 515.84eV±0.2eV
V ³⁺ : 515.29 eV±0.2 eV
<Measurement conditions>
ThermoFisher's ESCALAB220IXL was used for XPS measurement, Al was used as the X-ray source, and the peak position was standard-corrected with the CC bond of C1S as 284.8 eV. After confirming that the sample for evaluation was set in the apparatus and reached a high vacuum, measurement was performed under the conditions of an accelerating voltage of 10 kV, an emission current of 10 mA, and the number of scans of 30 times.
<Calculation conditions>
After the scan integration, peak separation was performed to confirm the presence or absence of V ³⁺ , V ⁴⁺ , and V ⁵⁺ peaks.
[3] Number of vanadium cations The surface of the denitration catalyst obtained in the example was subjected to SEM-EDS (energy dispersive X-ray spectroscopy) measurement under the following conditions.
<Measurement conditions>
The SEM measurement used JEOL's JSM6010LA, and W was used as the X-ray source. The denitration catalysts obtained in the examples were processed into fragments, and the surfaces to be the denitration reaction surfaces (the outer surface in the case of pellets, the outer surface of partition walls in the case of honeycombs) were measured. The acceleration voltage is adjusted to 20 kV-15 kV, and the SS is adjusted to 4 nm. After that, the sample was magnified to 1,500,000 times, the analysis position was probe-tracked, EDS-line analysis was performed so that the measurement position could be traced, and then the composition conversion was performed by the ZAF method. The particle size of the composite oxide containing V and Mo was calculated from the peaks obtained there. After adjusting the beam diameter to this particle diameter, the beam was magnified 1,500,000 times, the analysis position was probe-tracked, and four or more points of Ti, V, and Mo were analyzed. This was repeated at different measurement points, and a total of 20 or more points were analyzed.
<Calculation method>
From the obtained data, 20 locations where all Ti, V, and Mo were detected were specified, and the average value of the number of cations of V at each location was calculated, and this was used as the number of cations in the present invention. This number of cations is calculated assuming that the number of oxygens in the fully oxidized state (V ₂ O ₅ in the case of V) is 24, and is 0 in the case of the fully oxidized state.
[4] Specific surface area The denitration catalyst obtained in the example was pulverized to prepare an evaluation sample. This evaluation sample (0.2 g) was placed in a measurement cell and subjected to degassing treatment at 300° C. for 60 minutes in a nitrogen gas stream. The temperature of the liquid nitrogen was maintained in the chamber, and nitrogen was allowed to equilibrate to the sample. Next, the temperature of the sample was gradually raised to room temperature while the mixed gas was flowing, and the amount of nitrogen desorbed during this time was detected, and the specific surface area of the sample was measured using a calibration curve prepared in advance.
[5] Crystal structure of titanium oxide and crystallite size of (101) plane The denitration catalyst obtained in the example was pulverized in a mortar and subjected to X-ray diffraction using an X-ray diffractometer (manufactured by Rigaku Corporation, RINT2100). A pattern was obtained to identify the crystal type.
Further, by the method described above, the full width at half maximum of the peak of the (101) plane near 2θ = 25.27 degrees (near 2θ = 25.27 degrees) in the obtained X-ray diffraction pattern was measured, and the Scherrer formula , the crystallite size was determined.
[6] Denitrification performance (selective reduction catalyst (SCR) activity)
The denitration catalysts obtained in the examples were cut into the following catalyst shapes to prepare samples for evaluation. This was filled in a flow reactor, and the denitrification rate was evaluated. Specifically, the denitrification rate was calculated using the following formula from the NO _x concentrations before and after contact with the catalyst measured under the following conditions. The concentration of nitrogen oxide NO _x in the gas before and after contact with the catalyst was measured with a chemiluminescent nitrogen oxide analyzer (ECL-88AO, manufactured by Anatec Yanaco Co., Ltd.).
Denitrification rate (%) = [NO x (ppm) in pre-contact gas - NO _x (ppm) in post-contact gas] / NO _x (ppm) in pre-contact gas _x 100
<Test conditions>
・Catalyst shape: 7 × 7 meshes, length 300 mm
・Reaction temperature: 200°C
・SV: 18750h ^-1
・Gas composition: NO _x =100 ppm, NH ₃ =100 ppm, O ₂ =2%, H ₂ O=1
0%, _N2 = balance

[Example 1]
6000 g of water, 1096.26 g of monoethanolamine as a complexing agent, and 2011.49 g of ammonium metavanadate were prepared. After mixing these, the temperature was raised to 80 to 90° C. and stirring was continued for 2 hours. This was cooled to 40-60° C., 765.54 g of ammonium molybdate was added, and stirring was continued for 5 minutes. After that, 2520 g of sulfuric acid (concentration: 25% by mass) was added to obtain a solution containing vanadium and molybdenum (mother liquor preparation step).

17590 g of titanium dioxide (Tronox: G5) and the solution prepared in the mother liquor preparation step were kneaded with a kneader for 30 minutes (mixing step). 1480 g of aqueous ammonia (concentration: 15% by mass) was added as a precipitant to the obtained kneaded product, and kneaded for 45 minutes. After that, 2400 g of glass fiber was added as a reinforcing material and kneaded for 10 minutes. Furthermore, 560 g of Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a plasticizer and kneaded for 20 minutes to obtain molding clay (reaction step).

Using a screw vacuum extruder equipped with a honeycomb extrusion die, the molding clay obtained in the above-described reaction step was molded into a honeycomb (molding step). After the honeycomb was dried for a sufficient amount of time, it was dried for 2 days while being blown with hot air at 60°C. A denitration catalyst having a cell pitch of 2.8 mm and a wall thickness of 0.5 mm was obtained (calcination step). For this denitration catalyst, the above-described measurements were carried out. Table 1 shows the results. FIG. 1 shows the XPS spectrum of this denitration catalyst.

[Example 2: Increased molybdenum and increased sulfuric acid usage]
A denitration catalyst was prepared in the same manner as in Example 1, except that the amount of sulfuric acid added was 3650 g and the amount of titanium dioxide added was 17590 g. For this denitration catalyst, the above-described measurements were carried out. Table 1 shows the results. An SEM image of this denitration catalyst is shown in FIG.

[Example 3: Change type of titanium dioxide, increase firing temperature by 20°C]
The amount of ammonium molybdate added was 1786 g, the titanium dioxide was MC90 manufactured by Ishihara Sangyo Co., Ltd., and the amount added was 16450 g, the amount of ammonia water added was 1304 g, and the firing temperature was 470 ° C. A denitration catalyst was prepared in the same manner as in Example 1, except that For this denitration catalyst, the above-described measurements were carried out. Table 1 shows the results.

[Example 4: Vanadium increase]
Denitration was performed in the same manner as in Example 1, except that the amount of monoethanolamine added was 1421.03 g, the amount of ammonium metavanadate added was 2586.20 g, and the amount of titanium dioxide added was 18570 g. A catalyst was prepared. For this denitration catalyst, the above-described measurements were carried out. Table 1 shows the results.

[Comparative Example 1: Sulfuric acid not used]
3000 g of water, 330 g of monoethanolamine as a complexing agent, and 691.3 g of ammonium metavanadate were prepared. After mixing these, the temperature was raised to 80 to 90° C. and stirring was continued for 2 hours. This was cooled to 40-60° C. to prepare a solution.

18330 g of titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd.: MC90), 1411.99 g of ammonium metavanadate, 809.82 g of ammonium molybdate, and aqueous ammonia (concentration: 15% by mass) were kneaded for 30 minutes in a kneader. After that, the solution prepared as described above was added and kneaded for 30 minutes. Further, 1710 g of glass fiber was added as a reinforcing material and kneaded for 10 minutes. Further, 300 g of Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a plasticizer and kneaded for 20 minutes to obtain molding clay.

The resulting molding clay was then molded into a honeycomb shape with a screw extruder. After drying the compact, it was calcined in an electric furnace at 470° C. for 5 hours to obtain a denitration catalyst. For this denitration catalyst, the above-described measurements were carried out. Table 1 shows the results.

Claims (4)

including vanadium and molybdenum composite oxides,
The composite oxide is a mixed valence compound containing trivalent, tetravalent and pentavalent vanadium,
The number of vanadium cations contained in the composite oxide is 0.7 or more,
The composite oxide is bonded to the surface of the titanium oxide,
Denitrification catalyst. 2. The denitrification catalyst according to claim 1, wherein the sulfur content (in terms of _SO4 ) is in the range of 0.1% by mass or more and 5% by mass or less. 3. The denitration catalyst according to claim 1 or 2, having a specific surface area of less than 100 m< ² >/g. A method for producing a denitration catalyst comprising the following steps 1) to 5).
1) A mother liquor preparation step of mixing water, sulfuric acid, a vanadium raw material, a molybdenum raw material and a complexing agent to prepare a mother liquor 2) A mixing step of mixing titanium oxide and the mother liquor to prepare a mixture 3) The mixture and precipitation 4) a reaction step of preparing a molding clay in which a coprecipitate of vanadium and molybdenum is bonded to the titanium oxide by mixing with an agent; A calcining step of calcining the compact to prepare a denitration catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of the titanium oxide.

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