Denitrification catalyst

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]

[0001] This invention relates to a denitrification catalyst capable of purifying nitrogen oxides in exhaust gas. [Background technology]

[0002] Conventionally, nitrogen oxides (NOx) in exhaust gas x As a denitrification catalyst that selectively reduces and removes nitrogen oxides with a reducing agent such as ammonia, honeycomb-shaped catalyst molded products, in which active components such as tungsten oxide and vanadium oxide are supported on a titanium oxide support, are used industrially (Patent Document 1). In recent years, they have also been used as catalysts to remove nitrogen oxides from exhaust gas of boilers, waste incinerators, etc., and operation at temperatures below approximately 200°C is desired from the viewpoint of suppressing the generation of dioxins. As a denitrification catalyst that solves this problem, denitrification catalysts such as those described in Patent Documents 2 and 3 have been proposed, and there is a growing demand for highly active denitrification catalysts, especially those that are highly active at low temperatures. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-81995 [Patent Document 2] Japanese Patent Application Publication No. 11-165068 [Patent Document 3] Special Publication No. 2007-520327 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to provide a highly active denitrification catalyst. [Means for solving the problem]

[0005] The present invention is a denitration catalyst characterized in that it comprises a composite oxide of vanadium and molybdenum, said composite oxide is a mixed-valence compound containing trivalent, tetravalent and pentavalent vanadium, the number of vanadium cations contained in said composite oxide is 0.7 or more, and said composite oxide is bonded to the surface of a titanium oxide. Effects of the Invention

[0006] The denitration catalyst of the present invention has high NO x selective reduction activity, so that NO can be efficiently removed not only in a high temperature range but also in a low temperature range of about 200°C or lower x . Brief Description of Drawings

[0007] [Figure 1] Fig. 1 is an X-ray photoelectron spectroscopy (XPS) spectrum of the denitration catalyst obtained in Example 1. [Figure 2] Fig. 2 is a scanning electron microscope (SEM) image of the denitration catalyst obtained in Example 2. Mode for Carrying Out the Invention

[0008] Embodiments of the present invention will be described in further detail below.

[0009] [Denitration Catalyst of the Present Invention] The denitration catalyst of the present invention comprises a composite oxide of vanadium and molybdenum, said composite oxide is a mixed-valence compound containing trivalent, tetravalent and pentavalent vanadium, the number of vanadium cations contained in said composite oxide is 0.7 or more, and said composite oxide is bonded to the surface of a titanium oxide. The present invention provides a denitration catalyst with enhanced NO x selective reduction activity by controlling the number of vanadium cations within a certain range.

[0010] A composite oxide of vanadium and molybdenum is a mixed-valence compound 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 bonding state to the surface of titanium oxide. The valence state of vanadium can be defined by the cation number, and by setting this cation number to 0.7 or more, the NO x selective reduction activity is enhanced. 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 a band structure optimal for the selective reduction activity of NO x . Furthermore, in the denitration catalyst of the present invention, vanadium having different valences is dispersed in the composite oxide, so the dispersibility of vanadium is higher compared to conventional denitration catalysts that simply contain vanadium oxides having different valences. Therefore, the denitration catalyst of the present invention has higher selective reduction activity for NO x compared to conventional denitration catalysts.

[0011] The cation number of vanadium contained in the composite oxide of vanadium and molybdenum 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 particularly preferably in the range of 1 or more and 1.4 or less. When the cation number of vanadium is within this range, the selective reduction activity for NO x is further improved.

[0012] The composite oxide of vanadium and molybdenum is bonded to the surface of titanium oxide. This is different from a composite oxide in which vanadium, molybdenum, and titanium are mixed in the same crystal structure; the composite oxide of vanadium and molybdenum is bonded to the surface of titanium oxide via oxygen. Thereby, the phase of the composite oxide and the phase of titanium oxide are clearly distinguished.

[0013] The titanium oxide is preferably titanium dioxide, and more preferably has an anatase-type crystal structure. When such titanium oxide is used, NO xSelective reduction activity tends to be high. Furthermore, the crystallite size of the titanium oxide, which has an anatase crystal structure, is preferably in the range of 5 nm to 40 nm, and more preferably in the range of 5 nm to 10 nm, as determined from the half-width of the diffraction peak of the (101) plane. When the crystallite size of the titanium oxide, which has an anatase crystal structure, is in this range, bonding with composite oxides containing vanadium and molybdenum becomes easier. The titanium oxide content 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 TiO2.

[0014] Conventionally, denitrification catalysts with a large specific surface area have been used for NO x It is known to have good selective reduction activity. In contrast, the denitrification catalyst of the present invention has good NO even with a small specific surface area. x It exhibits selective reduction activity. Specifically, at 100m 2 Even if it is less than / g, 50m 2 / g or more 95m 2 Even in the range of less than / g, good NO x It exhibits selective reducing activity.

[0015] The denitrification catalyst of the present invention may contain components other than the vanadium and molybdenum composite oxide. For example, it may contain vanadium oxide and molybdenum oxide. The vanadium content (in V2O5 equivalent), including the vanadium contained in the composite oxide, is preferably in the range of 1% to 20% by mass, more preferably in the range of 5% to 15% by mass, and particularly preferably in the range of 6% to 10% by mass. The molybdenum content (in MoO3 equivalent), including the molybdenum contained in the composite oxide, is preferably in the range of 0.5% to 15% by mass, more preferably in the range of 1% to 10% by mass, and particularly preferably in the range of 2% to 8% by mass. When the vanadium and molybdenum content is within this range, NO xSelective reduction activity tends to be high. In addition to vanadium and molybdenum, the catalyst may also contain metal components such as tungsten, chromium, manganese, iron, nickel, copper, silver, gold, palladium, yttrium, cerium, neodymium, indium, iridium, and antimony. These act as co-catalysts and affect catalytic performance, and their content (in terms of metal) is preferably 3% by mass or less.

[0016] The denitrification catalyst of the present invention preferably contains sulfur. The sulfur content (SO4 equivalent) is preferably in the range of 0.1% to 5% by mass, more preferably in the range of 0.5% to 4% by mass, and particularly preferably in the range of 0.5% to 3% by mass. The sulfur contained in the denitrification catalyst of the present invention affects the band structure of vanadium, and NO x It has a positive effect on selective reduction activity.

[0017] In addition to these components, inorganic components such as glass fibers, silica, and alumina may be included as reinforcing materials. These components enhance the moldability of the denitrification catalyst and maintain its strength.

[0018] The shape of the denitrification catalyst of the present invention may be a conventionally known shape such as a pellet or a honeycomb, and is preferably a honeycomb. Specifically, the outer diameter of the honeycomb is preferably in the range of 30 mm to 300 mm, and more preferably in the range of 50 mm to 200 mm. The length of the honeycomb is preferably in the range of 100 mm to 3000 mm, and more preferably in the range of 300 mm to 1500 mm. The through-holes of the honeycomb (hereinafter sometimes referred to as cell pitch) are preferably in the range of 1 mm to 15 mm, and more preferably in the range of 2 mm to 10 mm. The partition wall thickness of the honeycomb is preferably in the range of 0.1 mm to 2 mm, and more preferably in the range of 0.1 mm to 1.5 mm. The opening ratio of the honeycomb is preferably in the range of 60% to 85%, and more preferably in the range of 70% to 85%. When the shape of the honeycomb is within this range, the strength of the honeycomb structure is maintained while reducing NO per unit volume. x Selective reduction activity tends to increase.

[0019] The denitrification catalyst of the present invention is NO x Exhaust gas containing NO, especially from boilers or waste incinerators, x Ya SO x NO is produced by catalytic reduction of exhaust gas containing heavy metals and dust by adding a reducing agent such as ammonia. x It is suitably used in removal methods. Furthermore, it can be used at the reaction temperatures of conventionally known denitrification catalysts, for example, at reaction temperatures between 150°C and 400°C. In particular, the denitrification catalyst of the present invention exhibits high activity in the temperature range of 170°C to 270°C, and especially in the temperature range of 170°C to 200°C, it exhibits good NO removal. x It exhibits selective reducing activity.

[0020] [Method for producing the denitrification catalyst of the present invention] The method for producing the denitrification catalyst of the present invention is described below.

[0021] The denitrification catalyst of the present invention can be prepared, for example, by a manufacturing method comprising the following steps. 1) Mother liquor preparation process: Mix water, sulfuric acid, vanadium raw material, molybdenum raw material, and complexing agent to prepare the mother liquor. 2) Mixing step of mixing titanium oxide and the mother liquor to prepare a mixture. 3) A reaction step in which the mixture and the precipitant are mixed to prepare a molding clay in which vanadium and molybdenum coprecipitates are bonded to the titanium oxide. 4) Molding process for preparing a molded body by molding the molding clay. 5) A firing process in which the molded body is fired to prepare a denitrification catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of a titanium oxide.

[0022] The following details each step.

[0023] In the mother liquor preparation process, the mother liquor is prepared by dissolving vanadium raw materials, molybdenum raw materials, a complexing agent, and sulfuric acid in water. Here, vanadium and molybdenum serve as raw materials for forming the complex oxide. The complexing agent coordinates with vanadium or molybdenum ions to form a complex. Sulfuric acid is used to coordinate with titanium oxide. The mother liquor can be prepared by dissolving these raw materials in water.

[0024] For the vanadium and molybdenum raw materials, it is preferable to use soluble salts. For example, as the vanadium raw material, it is preferable to use vanadate, vanadium sulfate, or vanadium chloride, and in particular, ammonium metavanadate is preferred. Alternatively, vanadium oxide may be dissolved in acid. As the molybdenum raw material, it is preferable to use molybdate, molybdenum sulfate, or molybdenum chloride, and in particular, ammonium molybdate is preferred. Alternatively, molybdenum oxide may be dissolved in acid. Furthermore, these may be used individually or in combination of two or more. The amount of vanadium and molybdenum raw materials added is appropriately adjusted according to the composition of the final denitrification catalyst.

[0025] The complexing agent is preferably a compound having an amine and a hydroxyl group, more preferably an alkanolamine, and particularly preferably ethanolamine. These complexing agents coordinate to vanadium ions or molybdenum ions in the mother liquor to form a complex and stabilize them. They also have the function of ligand exchange with sulfuric acid coordinated to titanium oxide in a later step. Therefore, it is preferable to add the complexing agent after dissolving the vanadium and molybdenum raw materials in water. At this time, the amount of complexing agent added is preferably in the range of 0.1 moles to 6 moles, and more preferably in the range of 0.5 moles to 3 moles, relative to the molar amount of vanadium and molybdenum. In this way, the vanadium and molybdenum ions are stabilized by adding the amount of complexing agent necessary to form the complex.

[0026] Sulfuric acid is added with the aim of coordinating to the surface of the titanium oxide, which will be added in a later step, and immobilizing vanadium and molybdenum on the surface of the titanium oxide through a ligand exchange reaction with the vanadium and molybdenum complex. Therefore, the amount of sulfuric acid added is preferably in the range of 0.001 moles to 0.1 moles, and more preferably in the range of 0.01 moles to 0.05 moles, relative to the molar amount of titanium. Since the purpose is to coordinate to the surface of the titanium oxide, it is not a problem if the amount of sulfuric acid added is small relative to the molar amount of titanium.

[0027] In this mother liquor preparation step, other soluble components may be added. For example, a raw material containing the aforementioned co-catalyst component may be dissolved.

[0028] In the mixing step, the mother liquor prepared in the aforementioned mother liquor preparation step is mixed with titanium oxide to prepare a mixture. Here, the sulfuric acid contained in the mother liquor coordinates to the surface of the titanium oxide. The titanium oxide is preferably titanium dioxide, and more preferably anatase-type crystalline structure. When such titanium oxide is used, NO xSelective reduction activity tends to be high. Furthermore, the crystallite size of the titanium oxide with an anatase crystal structure is preferably in the range of 10 nm to 40 nm, and more preferably in the range of 5 nm to 10 nm, as determined from the half-width of the diffraction peak of the (101) plane. When the crystallite size of the titanium oxide with an anatase crystal structure is in this range, bonding with composite oxides containing vanadium and molybdenum becomes easier. The amount of titanium oxide added is adjusted as appropriate according to the composition of the final denitrification catalyst.

[0029] Conventional mixing methods can be used. For example, a kneader, a high-speed mixer, or a ball mill can be used. These methods are appropriately selected depending on the amounts of mother liquor and titanium oxide. If the mixture becomes clay-like and puts a load on the equipment, it is preferable to use a kneader or a high-speed mixer.

[0030] In the reaction step, the mixture and a precipitating agent are mixed to prepare a molding clay in which a coprecipitate of vanadium and molybdenum is bonded to the surface of the titanium oxide. In this step, the mother liquor components contained in the mixture are neutralized, and a coprecipitate of vanadium and molybdenum is formed. At this time, the complexing agent is coordinated to the surface of the coprecipitate, and this complexing agent exchanges ligands with the sulfuric acid coordinated to the surface of the titanium oxide, thereby creating a bond between the coprecipitate and the surface of the titanium oxide.

[0031] Conventional precipitating agents can be used. For example, precipitating agents such as sodium carbonate, soda ash, and aqueous ammonia can be used. The amount of precipitating agent added is adjusted as appropriate so that the pH of the mother liquor contained in the mixture is in the range of 6 to 9. If the mixture is clay-like and it is difficult to measure the pH, the amount of precipitating agent needed to neutralize the mother liquor should be determined experimentally beforehand, and the amount added should be adjusted accordingly. If the mixture is not clay-like, the moisture content should be adjusted, a binder should be added, etc., to adjust it into a molding clay suitable for molding.

[0032] In the molding process, the molding clay is molded to prepare a molded body. It can be molded into conventionally known shapes such as pellets or honeycomb. For applications as a denitrification catalyst, molding into a honeycomb is preferable. Conventional known methods can be used for molding; for example, it can be molded into pellets or honeycomb using an extrusion molding machine. The molded body should be dried using conventionally known methods to prevent cracking or other damage.

[0033] In the firing process, the molded body is fired to prepare a denitrification catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of the titanium oxide. Conventional firing methods can be used. For example, firing in air using a heating furnace such as an electric furnace or a gas furnace can be used. The firing temperature is preferably between 300°C and 500°C. The firing time depends on the firing temperature, but is generally within the range of 1 hour to 48 hours. [Examples]

[0034] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited in any way to the examples provided.

[0035] [Measurement method] The measurement methods adopted in this application are described below. [1] Composition The denitrification catalyst obtained in the examples was powdered to prepare an evaluation sample. A solution was prepared by dissolving this in acid, and the composition of various components was calculated using inductively coupled plasma atomic emission spectroscopy (instrument name: ICPS-8100). [2] Valence of vanadium The denitrification catalysts obtained in the examples were prepared as evaluation samples by fragmenting them so that the reaction surface (the outer surface in the case of pellets, or the outer surface of the partitions in the case of honeycomb) could be measured. These samples were placed on a sample stage and X-ray photoelectron spectroscopy (XPS) was performed under the following conditions. The spectra obtained from these measurements were analyzed, and if peaks were detected within the following ranges, it was determined that the catalyst contained vanadium of these valencies. V5+ :517.20eV±0.2eV V 4+ :515.84eV±0.2eV V 3+ :515.29eV±0.2eV <Measurement conditions> XPS measurements were performed using a ThermoFisher ESCALAB220IXL, with Al as the X-ray source. The peak position was corrected to a reference value of 284.8 eV for the CC coupling of C1S. After setting the evaluation sample in the instrument and confirming that high vacuum had been achieved, measurements were taken under the conditions of an acceleration voltage of 10 kV, an emission current of 10 mA, and 30 scans. <Calculation conditions> After scan integration, peak separation is performed, V 3+ , V 4+ , V 5+ Check for the presence or absence of a peak. [3] Number of vanadium cations The surface of the denitrification catalyst obtained in the examples was measured by SEM-EDS (energy-dispersive X-ray spectroscopy) under the following conditions. <Measurement conditions> SEM measurements were performed using JEOL's JSM6010LA, with wtr (W) as the X-ray source. The denitrification catalyst obtained in the examples was processed into fragments, and the surface that constitutes the denitrification reaction (the outer surface for pellets, or the outer surface of the partitions for honeycomb structures) was measured. The acceleration voltage was adjusted to 20kV-15kV, and the SS (sulfide filtration) was adjusted to 4nm. Then, the image was magnified up to 1.5 million times, the analysis position was probe-tracked, and EDS-line analysis was performed to trace the measurement position, followed by compositional transformation using the ZAF method. From the resulting peaks, the particle size of the composite oxide containing v and molybdenum (V) and molybdenum (Mo) was calculated. After adjusting the beam diameter to this particle size, the image was magnified up to 1.5 million times, the analysis position was probe-tracked, and point analysis of Ti, v, and molybdenum (Ti) was performed at four or more locations. This was repeated at different measurement locations, resulting in a total of more than 20 point analyses. <Calculation method> From the obtained data, 20 locations where Ti, V, and Mo were all detected were identified, and the average number of V cations at each location was calculated and used as the cation number in this invention. This cation number is calculated assuming that the number of oxygen atoms in the completely oxidized state (V2O5 in the case of V) is 24, and in the completely oxidized state it is 0. [4] Specific surface area The denitrification catalyst obtained in the examples was pulverized to prepare an evaluation sample. This evaluation sample (0.2 g) was placed in a measuring cell and degassed at 300°C for 60 minutes in a nitrogen gas stream. Then, the sample was kept at liquid nitrogen temperature in a mixed gas stream of 30% nitrogen and 70% helium by volume, allowing nitrogen to be adsorbed to equilibrium on the sample. Next, the temperature of the sample was gradually raised to room temperature while flowing the mixed gas, and the amount of nitrogen desorbed during this time was detected. The specific surface area of ​​the sample was then measured using a pre-prepared calibration curve. [5] Crystal structure of titanium oxide and crystallite size of the (101) plane The denitrification catalysts obtained in the examples were pulverized in a mortar, and the X-ray diffraction pattern was obtained using an X-ray diffractometer (Rigaku Corporation, RINT2100) to identify the crystal type. Furthermore, using the method described above, the full width at half maximum of the peak in the (10¹) plane (near 2θ = 25.27 degrees) in the obtained X-ray diffraction pattern was measured, and the crystallite size was determined using Scherrer's formula. [6] Denitrification performance (selective reduction catalyst (SCR) activity) The denitrification catalyst obtained in the examples was cut into the following catalyst shapes to prepare evaluation samples. These were packed into a flow-through reactor, and the denitrification rate was evaluated. Specifically, NO before and after catalyst contact was measured under the following conditions. x The denitrification rate was calculated from the concentration using the following formula. Note that nitrogen oxides (NOx) in the gas before and after catalyst contact were also used. x The concentration was measured using a chemiluminescent nitrogen oxide analyzer (ECL-88AO, manufactured by Anatech Yanaco Co., Ltd.). Denitrification rate (%) = [NOx in gas before contact] x (ppm) - NO in gas after contact x (ppm)] / NOx in gas before contact x (ppm) × 100 <Test Conditions> • Catalyst shape: 7x7 mesh, 300mm length Reaction temperature: 200℃ ·SV:18750h -1 • Gas composition: NO x =100ppm, NH3=100ppm, O2=2%, H2O=1 0%, N2 = Balance

[0036] [Example 1] 6000g of water, 1096.26g of monoethanolamine as a complexing agent, and 2011.49g of ammonium metavanadate were prepared. After mixing these, the temperature was raised to 80-90°C and stirring was continued for 2 hours. This was then cooled to 40-60°C, 765.54g of ammonium molybdate was added, and stirring was continued for 5 minutes. Subsequently, 2520g of sulfuric acid (concentration: 25% by mass) was added to obtain a solution containing vanadium and molybdenum (mother liquor preparation step).

[0037] 17590g of titanium dioxide (Tronox: G5) and the solution prepared in the aforementioned mother liquor preparation step were kneaded in a kneader for 30 minutes (mixing step). 1480g of aqueous ammonia (concentration: 15% by mass) was added to the resulting mixture as a precipitating agent and kneaded for 45 minutes. Then, 2400g of glass fiber was added as a reinforcing material and kneaded for 10 minutes. Furthermore, 560g of metholose (Shin-Etsu Chemical Co., Ltd.) was added as a plasticizer and kneaded for 20 minutes to obtain molding clay (reaction step).

[0038] Using a screw-type vacuum extruder equipped with a honeycomb extrusion die, the molding clay obtained in the reaction process described above was molded into a honeycomb (molding process). After drying this honeycomb for a sufficient amount of time, it was dried for two days with hot air at 60°C, then both ends in the axial direction (longitudinal direction) were trimmed, and it was fired in an electric furnace in an atmospheric atmosphere at 450°C for 5 hours to obtain a denitrification catalyst with a cell pitch of 2.8 mm and a wall thickness of 0.5 mm (firing process). The aforementioned measurements were performed on this denitrification catalyst. The results are shown in Table 1. The XPS spectrum of this denitrification catalyst is shown in Figure 1.

[0039] [Example 2: Increased molybdenum content, increased sulfuric acid usage] A denitrification 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. The aforementioned measurements were performed on this denitrification catalyst. The results are shown in Table 1. Figure 2 shows an SEM image of this denitrification catalyst.

[0040] [Example 3: Change in titanium dioxide type, increase in firing temperature by 20°C] Except for the addition of 1786g of ammonium molybdate, 16450g of MC90 titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd.), 1304g of aqueous ammonia, and a calcination temperature of 470°C, a denitrification catalyst was prepared in the same manner as in Example 1. The aforementioned measurements were performed on this denitrification catalyst. The results are shown in Table 1.

[0041] [Example 4: Increased vanadium content] A denitrification catalyst was prepared 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. The aforementioned measurements were performed on this denitrification catalyst. The results are shown in Table 1.

[0042] [Comparative example 1: No sulfuric acid used] 3000g of water, 330g of monoethanolamine as a complexing agent, and 691.3g of ammonium metavanadate were prepared. After mixing these, the temperature was raised to 80-90°C and stirring was continued for 2 hours. This was then cooled to 40-60°C to prepare the solution.

[0043] 18330g of titanium dioxide (manufactured by Ishihara Sangyo Co., Ltd.: MC90), 1411.99g of ammonium metavanadate, 809.82g of ammonium molybdate, and aqueous ammonia (concentration: 15% by mass) were kneaded in a kneader for 30 minutes. Then, the solution prepared as described above was added and kneaded for another 30 minutes. Furthermore, 1710g of glass fiber was added as a reinforcing material and kneaded for 10 minutes. Finally, 300g of metholose (manufactured by Shin-Etsu Chemical Co., Ltd.) was added as a plasticizer and kneaded for another 20 minutes to obtain molding clay.

[0044] Next, the obtained molding clay was formed into a honeycomb shape using a screw-type extruder. After drying this molded body, it was fired in an electric furnace at 470°C for 5 hours to obtain a denitrification catalyst. The aforementioned measurements were performed on this denitrification catalyst. The results are shown in Table 1.

[0045] [Table 1]

Claims

1. It contains a composite oxide of vanadium and molybdenum, The aforementioned 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 aforementioned composite oxide is bonded to the surface of the titanium oxide, The sulfur content (in SO₄ equivalent) is in the range of 0.1% by mass or more and 5% by mass or less. Denitrification catalyst.

2. Specific surface area of ​​100 m² ２ The denitrification catalyst according to claim 1, wherein the amount is less than / g.

3. A method for producing a denitrification catalyst comprising the following steps 1) to 5). 1) Mother liquor preparation process: Mix water, sulfuric acid, vanadium raw material, molybdenum raw material, and complexing agent to prepare the mother liquor. 2) Mixing step of mixing titanium oxide and the mother liquor to prepare a mixture. 3) A reaction step in which the mixture and the precipitant are mixed to prepare a molding clay in which vanadium and molybdenum coprecipitates are bonded to the titanium oxide. 4) Molding process for preparing a molded body by molding the molding clay. 5) A firing process in which the molded body is fired to prepare a denitrification catalyst in which a composite oxide of vanadium and molybdenum is bonded to the surface of a titanium oxide.

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