KR100894493B1 - Catalyst for treating exhaust gas and method for treating exhaust gas - Google Patents

Abstract

An exhaust gas treatment catalyst for decomposing and removing harmful substances in exhaust gas containing titanium oxide and other catalytically active components, wherein the ratio (B / L) of bronsteadic acid (B) and Lewis acid (L) is An exhaust gas treating catalyst and an exhaust gas treating method using the catalyst are in the range of 0/1 to 10/1.

Description

Catalyst for treating exhaust gas and method for treating exhaust gas

1 is an X-ray diffraction diagram of the Ti-Si composite oxide obtained in Example 1. FIG.

2 is an FT-IR spectrum of the adsorbed pyridine of the catalyst (1) obtained in Example 1. FIG.

3 is an X-ray diffraction diagram of the Ti-Si composite oxide obtained in Comparative Example 1. FIG.

4 is an FT-IR spectrum of the adsorbed pyridine of the catalyst (5) obtained in Comparative Example 1. FIG.

5 is an X-ray diffraction diagram of the anatase-type titania oxide powder used in Comparative Example 2. FIG.

6 is an FT-IR spectrum of the adsorbed pyridine of the Ti-Si composite oxide (e) obtained in Example 6. FIG.

7 is an FT-IR spectrum of the adsorbed pyridine of the Ti-Si composite oxide (h) obtained in Comparative Example 3. FIG.

The present invention relates to a catalyst for treating exhaust gas and a method for treating exhaust gas. Specifically, the present invention relates to an exhaust gas treating catalyst and a catalyst suitable for decomposing and removing hazardous substances such as nitrogen oxides and dioxins contained in exhaust gas. The present invention relates to a method for treating exhaust gas using a catalyst.

Many catalysts and treatment methods have already been proposed to decompose and remove harmful substances such as nitrogen oxides and dioxins contained in the exhaust gas.

For example, a catalyst which selectively reacts nitrogen oxides in exhaust gas with ammonia and reacts them selectively to (a) a sulfur-containing complex containing sulfur, titanium and silicon, or titanium, zirconium and silicon. A catalyst for removing nitrogen oxides containing oxides of at least one element selected from oxides, (b) vanadium oxides, (c) tungsten, molybdenum, tin and cerium has been proposed (for example, Japanese Patent Publication No. 62 -14339).

In view of the specific surface area and the amount of solid acid of the catalyst, these physical properties and the catalyst composition are specified in the catalyst for the exhaust gas treatment, specifically, oxides such as vanadium, tungsten, and molybdenum on a carrier such as a titanium-silicon composite oxide. It is proposed that the catalyst has a specific surface area of 10 m 2 / g or more and a solid acid amount of 0.36 mmol / g or more that is effective for removing harmful substances such as nitrogen oxides and dioxins contained in the exhaust gas (for example, , Japanese Patent No. 3457917).

However, the conventional catalyst for treating exhaust gas is not sufficiently satisfactory with respect to its performance, but a catalyst for more efficiently removing harmful substances such as nitrogen oxides and dioxins contained in the exhaust gas, for example, nitrogen. In the case of oxides, development of catalysts for exhaust gas treatment having higher denitrification efficiency is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas treating catalyst which is very suitable for removing harmful substances such as nitrogen oxides and dioxins contained in the exhaust gas and a method for efficiently treating the exhaust gas using the catalyst. have.

MEANS TO SOLVE THE PROBLEM In order to achieve the said objective, the present inventors made extensive research, and came to acquire the following knowledge. That is, on the surface of the solid catalyst, there are generally Bronsted acid points that donate protons and Lewis acids that accept electron pairs. For example, in the case of denitrification, both Bronsted acid points and Lewis acid points contribute to denitrification activity. In particular, it was found that the highest denitrification effect was obtained when the abundance ratio of the bronsted acid point and the Lewis acid point were in a specific range.

Further, in the exhaust gas treatment catalyst containing titanium oxide, the amount of solid acid having an acid strength of pKa ≦ + 3.3 as the titanium oxide is 0.3 mmol / g or more, and Bronsted provides a solid acid point of proton. By distinguishing between the acid point and the Lewis acid point accommodating the electron pair, by using a ratio (B / L) of the amount of Bronstead acid (B) and the amount of Lewis acid (L) is 0/1 to 1/1, It was found that a catalyst having excellent decomposition performance of harmful substances was obtained.

This invention is completed based on the said knowledge, and is as follows.

(1) Exhaust gas treatment catalyst for decomposing and removing harmful substances in exhaust gas containing titanium oxide and other catalytically active ingredients, wherein the ratio of Bronsted acid (B) and Lewis acid (L) (B / L) is in the range of 0/1 to 10/1, the catalyst for exhaust gas treatment.

(2) The catalyst as described in said (1) whose said ratio is 0/1-9/1.

(3) The catalyst according to the above (1), wherein the titanium oxide is titanium oxide.

(4) The catalyst according to the above (1), wherein the titanium oxide is a composite oxide of titanium with at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten.

(5) The catalyst according to the above (1), wherein the titanium oxide is a composite oxide of titanium with at least one element selected from the group consisting of aluminum, silicon, chromium and zirconium.

(6) The catalyst according to the above (1), wherein the titanium oxide is a composite oxide of titanium with at least one element selected from the group consisting of aluminum, silicon, and zirconium.

(7) The catalyst according to the above (1), wherein the other catalytically active component is at least one element selected from the group consisting of vanadium, tungsten and molybdenum or a compound thereof.

(8) Titanium content in the said titanium-based composite oxide is 40-95 mass%, and the said other catalytically active component is 60-5 mass% (These totals are 100 mass%), It is described in said (1). catalyst.

(9) The catalyst according to the above (1), wherein the content of the titanium oxide is 75 to 99.9 mass% based on the total amount of the catalyst.

(10) The catalyst according to the above (1), further containing sulfur.

(11) The catalyst according to the above (1), wherein the ratio (B / L) of the titanium oxide is 0/1 to 1/1, and the amount of solid acid having a pKa ≦ + 3.3 is 0.3 mmol / g or more.

(12) The catalyst according to the above (11), wherein the amount of solid acid having a pKa ≦ + 3.3 is 0.3 to 0.8 mmol / g.

The catalyst as described in said (10) whose content of the said sulfur is 0.01-3 mass% with respect to the gross mass of a catalyst.

(14) The addition of an aqueous ammonia solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten to an acidic solution containing a titanium compound produces a precipitate. The method for producing a catalyst according to the above (1), wherein the obtained titanium-based composite oxide is used after a process in which the time from starting to adding the total amount thereof is 40 minutes or more.

(15) adding an acidic solution containing a titanium compound to an aqueous ammonia solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten to form a precipitate The method for producing a catalyst according to the above (1), wherein the obtained titanium-based composite oxide is used after passing through the step of starting the process and adding the total amount to 40 minutes or more.

(16) In the acidic solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten and a titanium compound, an aqueous solution of ammonia is added to generate a precipitate to start addition. And a titanium-based composite oxide obtained after the step of adding the total amount thereof to 40 minutes or more is used. The method for producing a catalyst according to the above (1), wherein the obtained titanium-based composite oxide is used.

(17) In the aqueous ammonia solution, adding an acidic solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten and a titanium compound to produce a precipitate, the addition is started. And a titanium-based composite oxide obtained after the step of adding the total amount thereof to 40 minutes or more is used. The method for producing a catalyst according to the above (1), wherein the obtained titanium-based composite oxide is used.

(18) A method for treating an exhaust gas, wherein the exhaust gas containing the hazardous substance is brought into contact with the exhaust gas treating catalyst according to any one of (1) to (13) to decompose and remove the harmful substance.

"Hazardous substances" in the present invention means organic halogen compounds such as nitrogen oxides, chlorinated dioxins, brominated dioxins, polychlorinated biphenyls, chlorobenzenes, chlorophenols and chlorotoluene. The exhaust gas treatment when the toxic substance is nitrogen oxide is a so-called denitrification treatment, in which nitrogen oxide is reduced and decomposed using a reducing agent such as ammonia or urea. The catalyst for exhaust gas treatment of the present invention is particularly suitably used for reduction decomposition (denitrification) of nitrogen oxides.

The exhaust gas treating catalyst according to the present invention is an exhaust gas treating catalyst for decomposing and removing harmful substances in exhaust gas containing titanium oxide and other catalytically active ingredients. Bronstead acid (B) and Lewis acid The ratio (B / L) of (L) is in the range of 0/1 to 10/1, and is a catalyst for exhaust gas treatment.

The ratio (B / L) is 0/1 to 10/1, preferably 0/1 to 9/1, more preferably 0.1 / 1 to 8/1, most preferably 0.1 / 1 to 7 / It is in the range of 1. When the ratio (B / L) is less than 0/1 or more than 10/1, the treatment performance of the catalyst is lowered.

The term "titanium oxide" in the present invention means titanium oxide and a composite oxide of titanium with other metal elements. As a titanium oxide, anatase type titanium oxide, rutile type titanium oxide, or a mixture thereof is used. Representative examples of the composite oxide include at least one member selected from the group consisting of titanium (Ti), aluminum (Al), silicon (Si), chromium (Cr), zirconium (Zr), molybdenum (Mo), and tungsten (W). The complex oxide with an element of is mentioned. You may use it, mixing a titanium oxide and a titanium type complex oxide.

Among the titanium-based composite oxides, titanium (Ti), aluminum (Al), silicon (Si), chromium (Cr) and zirconium (Zr), particularly aluminum (Al), silicon (Si) and zirconium (Zr) selected from Complex oxides with at least one element which is used are suitably used. The composite oxide may be a binary composite oxide such as a Ti-Si composite oxide or a ternary composite oxide such as a Ti-Si-Zr composite oxide. In addition, "composite oxide" does not exhibit a specific inherent peak attributable to a substance other than titanium oxide in the X-ray diffraction pattern, and does not exhibit or exhibit an inherent peak attributable to anatase type titanium oxide for titanium oxide. It means a diffraction peak wider than that of the titanium oxide.

For molybdenum and tungsten, respectively, the total amount constitutes a titanium-based composite oxide together with titanium, the total amount is present in the catalyst in a form other than the titanium-based composite oxide, or a part thereof constitutes the titanium-based composite oxide. And the remainder may be included in the catalyst in other forms.

Representative examples of the composition of the catalyst for treating exhaust gas of the present invention are as follows.

(1) Ti-Si composite oxide + (V, W and / or Mo)

(2) Ti-Al composite oxide + (V, W and / or Mo)

(3) Ti-Zr composite oxides + (V, W and / or Mo)

(4) Ti-W composite oxide + (V, W and / or Mo)

(5) Ti-Si-Zr composite oxides + (V, W and / or Mo)

(6) Ti-Si-Mo composite oxide + (V and / or W)

(7) Ti-Si-Mo composite oxide + (V, W and / or Mo)

(8) Ti-Si-W composite oxide + (V and / or Mo)

(9) Ti-Si-W composite oxides + (V, W and / or Mo)

(10) Ti oxide + (V, W and / or Mo)

The amount of bronsted acid (B) and the amount of Lewis acid (L) can be accurately measured by infrared spectroscopy (FT-IR) using pyridine as a probe. Pyridine has an infrared absorption band derived from in-plane vibrations of the pyridine ring in the region of 1700-1400 cm ^-1 , and depends on whether pyridine is hydrogen-bonded (PyH), coordinating (PyL), or protonated (PyB). Absorption bands are significantly different. Among them, the absorption bands of PyL (near 1450 cm ^{- 1} ) and PyB (near 1540 cm ^{- 1} ) are due to the 19b oscillation mode of pyridine adsorbed at the Lewis acid and Bronsted acid points, respectively, and the peak area of PyB is PyL. By calculating the peak area ratio (B / L) divided by the peak area of, the ratio of the amount of bronsted acid to the amount of Lewis acid can be determined.

"Bronstead acid amount (B)" and "Lewis acid amount (L)" in the present invention are the peak areas derived from the Bronsted acid point measured by the following FT-IR analysis using pyridine as a probe, respectively. It means the peak area derived from the Lewis acid point.

FT-IR method

The PROTEGE460 made by Nikolesa is used as the FT-IR apparatus, and the diffusion reflection type in situ cell is attached thereto. 0.02 g of the sample pulverized to 100 mesh or less is left as a powder without dilution with KBr or the like in the sample table of the diffuse reflection cell, while flowing helium gas containing 5% by volume of oxygen (O ₂ ) at a flow rate of 40 ml / min. Heat to 400 ° C. and hold at 400 ° C. for 60 minutes. After cooling to 150 ° C while flowing helium gas, 10 μL of pyridine (microliter) is injected at 150 ° C to absorb pyridine into the sample. Thereafter, helium gas was flowed at 150 ° C. for 120 minutes to remove physisorbed pyridine from the sample, and then cooled to room temperature, and the FT-IR spectrum was measured at a resolution of 4 cm ⁻¹ . The amount of bronsted acid (B) is determined by integrating the range of 1515 to 1565 cm ⁻¹ of the obtained FT-IR spectrum and the amount of Lewis acid (L) to 1425 to 1465 cm ⁻¹ , respectively.

The ratio (B / L) of the amount of bronsted acid (B) and the amount of Lewis acid (L) is easily obtained from the amount of Bronsted acid (B) and the amount of Lewis acid (L) determined by the FT-IR analysis method. .

There is no restriction | limiting in particular in the composition of the catalyst for waste gas treatment of this invention, as long as the said ratio (B / L) exists in the range of 0/1-10/1. Especially, it is preferable to contain a titanium oxide and at least 1 sort (s) of element chosen from vanadium (V), tungsten (W), and molybdenum (Mo).

When the said ratio (B / L) is 0/1-1/1, the "titanium oxide" used by this invention is 0.3 mmol / g or more, Preferably 0.3-0.8 mmol of solid acid amount whose pKa <= 3.3 is used. / g, more preferably 0.35 ~ 0.7 mmol / g, still more preferably 0.4 ~ 0.6 mmol / g in the range. If the amount of solid acid having a pKa ≤ +3.3 is less than 0.3 mmol / g, adsorption of harmful substances on the catalyst surface is lowered, and as a result, the decomposition performance of harmful substances in the catalyst is lowered. The amount of solid acid is considered to be the total acid amount of Bronsted acid and Lewis acid on the titanium oxide surface.

The "solid acid amount of pKa≤ + 3.3" in the present invention is measured by the following method.

<Measuring method of solid acid content>

It is calculated | required by n-butylamine titration method using p-dimethylamino azobenzene as an indicator of pKa = + 3.3. 0.2 g of a powder sample dried at 120 DEG C for at least 3 hours is weighed with a precision balance, placed in a test tube, and about 20 ml of benzene is added thereto. A few drops of the solution in which the said indicator was dissolved in benzene was added, and it mixed with a stopper well, and it turns into red which is the acidic color of an indicator. A 0.13-mmol / ml benzene solution of n-butylamine was added to the microburette, and the sample discolored to yellow, which is the basic color of the indicator, as the end point of titration. The acid amount (mmol / g) is calculated.

Solid acid amount = (butylamine solution concentration (mmol / ml) x titration amount (ml)) / (sample mass (g))

In the case of the said amount of solid acid, the "titanium oxide" used by this invention has the ratio (B / L) of Bronsted acid amount (B) and Lewis acid amount (L) of 0/1-1/1, Preferably it is 0.1. / 1 to 1/1, more preferably in the range of 0.1 / 1 to 0.8 / 1. If the ratio (B / L) exceeds 1/1, the catalyst for exhaust gas treatment obtained using this titanium oxide is low in its decomposition performance of harmful substances and is not preferable.

Titanium oxide having pKa ≦ + 3.3 of the present invention having a solid acid amount of 0.3 mmol / g or more and a ratio (B / L) of Bronsted acid amount and Lewis acid amount in a range of 0/1 to 1/1 Although it can prepare according to the method, the preparation method is demonstrated below using the titanium type composite oxide of titanium and at least 1 sort (s) of element chosen from aluminum, silicon, and zirconium as a titanium-type oxide.

There is no restriction | limiting in particular about starting raw material, The compound generally used for preparation of the composite oxide containing titanium can be used.

As a titanium source, it can select suitably from inorganic titanium compounds, such as titanium tetrachloride and titanium sulfate, and organic titanium compounds, such as titanium oxalate and tetraisopropyl titanate, for example.

As an aluminum source, it can select suitably from inorganic aluminum compounds, such as aluminum nitrate and aluminum sulfate, and organic aluminum compounds, such as aluminum acetate, for example.

As a silicon source, it can select suitably from inorganic silicon compounds, such as colloidal silica, water glass, particulate silicon, silicon tetrachloride, a silica gel, and organosilicon compounds, such as tetraethyl silicate, for example.

As a zirconium source, it can select suitably from inorganic zirconium compounds, such as zirconium chloride and zirconium sulfate, and organic zirconium compounds, such as zirconium oxalate, for example.

In the titanium composite oxide of the present invention, for example, in the case of a titanium-silicon composite oxide, a silicon compound such as colloidal silica is dispersed in an aqueous ammonia solution to prepare a solution (A), and sulfuric acid is stirred in the solution (A) under stirring. The time from the start of dropwise addition of a solution of a titanium compound such as titanyl until the pH of the mixed solution reaches 8 is 40 minutes or more, preferably 40 to 1440 minutes, more preferably 60 to 1080 minutes, and more preferably. Preferably it is dripped so that it may become 90 to 720 minutes, and the obtained slurry is filtered, and after drying, it is obtained by baking at the temperature of 300-600 degreeC. In the case of a titanium-silicon-aluminum composite oxide, a solution of an aluminum compound in addition to the titanium compound is added dropwise to the solution (A), wherein the time from the start of dropping until the pH of the mixed solution reaches 8 is 40. Minutes or more, preferably 40 to 1440 minutes, more preferably 60 to 1080 minutes, even more preferably 90 to 720 minutes, and dropping the resulting slurry, further drying and firing at a temperature of 300 to 600 ℃ Just do it.

In the case of dropping an aqueous ammonia solution into a mixed solution of a titanium compound and a silicon compound, or dropping a solution of a titanium compound, a condition in which the time from the start of dropping until the pH of the mixed solution reaches 8 is less than 40 minutes. In the case of dropping at, there is a possibility that a titanium compound having the target acidity cannot be obtained and sufficient exhaust gas treatment performance may not be obtained.

The content of titanium in the titanium-based composite oxide is preferably 40 to 95 mass%, based on the total mass of titanium with at least one element selected from aluminum, silicon, chromium, zirconium, molybdenum and tungsten. Preferably it is 50-95 mass%, Especially preferably, it is 60-95 mass%. The content of the other elements is different depending on whether they are binary composite oxides or ternary composite oxides. In the former case, the content of the other elements is 5 to 60 mass%, preferably based on the total mass of titanium and other elements. Preferably it is 5-50 mass%, More preferably, it is 5-40 mass%, In the latter case, content of another element is 1-60 mass% with respect to the total mass of titanium and another element, Preferably it is 5 It is -50 mass%, More preferably, it is 5-40 mass% (However, the sum total of a titanium complex oxide and another catalytically active component is 100 mass%).

The content of the titanium oxide in the catalyst for exhaust gas treatment of the present invention is 75 to 99.9% by mass, preferably 80 to 99.5% by mass, more preferably 85 to 99% by mass, based on the total mass of the catalyst. If the content of the titanium oxide exceeds 99.9% by mass, the content of at least one element selected from vanadium, tungsten and molybdenum is too small, and the catalytic performance is lowered. If the content of the titanium oxide is less than 75% by mass, the content of elements such as vanadium The content becomes large and the improvement of the catalytic performance suitable for it is not recognized, but rather the catalyst cost rises, which is not preferable.

There is no restriction | limiting in particular about the shape of a titanium oxide, You may use the titanium oxide obtained by the above preparation method as it is, or a plate shape, a corrugated plate shape, a network shape, a honeycomb shape, a column shape, a spherical shape, a cylindrical shape, a pellet shape You may shape | mold and shape it suitably. The shape of the titanium oxide is generally determined in consideration of the shape of the finished catalyst.

The titanium-based composite prepared as described above is a catalyst for the exhaust gas treatment in which the ratio (B / L) of the bronsted acid amount (B) and the Lewis acid amount (L) of the present invention is in the range of 1/1 to 10/1. It is obtained by using an oxide and adding at least one element selected from vanadium, tungsten and molybdenum thereto. About this method, a precipitation method (coprecipitation method), a hydrolysis method, a sol-gel method, a deposition method, the kneading method, etc. can be used, for example. Specifically, it is added to an aqueous solution containing starting materials of vanadium, tungsten and / or molybdenum to the powder of titanium oxide, together with an organic or inorganic molding aid generally used for forming this kind, and mixed and kneaded. Heating to evaporate to form an extrudable paste, which is molded into a honeycomb or the like by an extruder, and then dried and fired at high temperature (preferably 200 to 600 ° C.) in air. As another method, the titanium oxide powder is previously formed into a spherical, cylindrical pellet, lattice honeycomb, or the like, and then fired, and then impregnated with an aqueous solution containing starting materials of vanadium, tungsten and / or molybdenum. The method can also be adopted. In addition, a method of directly kneading the powder of the titanium oxide with the powder of the oxide of vanadium, tungsten and / or molybdenum can be employed. In addition, a slurry is prepared by adding an aqueous solution of a compound containing vanadium, tungsten and / or molybdenum to a solution or slurry containing titanium or the like in the step of preparing a titanium oxide, or by filtration or the like in the step of preparing a titanium oxide. A method of adding, mixing, drying and baking an aqueous solution of a compound containing vanadium, tungsten and / or molybdenum to a cake obtained by removing moisture from the mixture may also be employed.

As the vanadium source, for example, vanadium compounds such as hydroxides, ammonium salts, oxalates, halides, sulfates and the like can be appropriately selected and used in addition to vanadium oxides.

As a tungsten source, it can select suitably from tungsten oxide, ammonium paratungstate, ammonium metatungstate, tungstic acid, etc., for example.

As the molybdenum source, any one may be used as long as it produces molybdenum oxide by firing, and for example, an oxide, hydroxide, ammonium salt, halide of molybdenum, and the like can be appropriately selected from ammonium paramolybdate, molybdate and the like. .

The content of vanadium, tungsten and / or molybdenum in the catalyst for exhaust gas treatment of the present invention is 0.1 to 25% by mass, preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, based on the total mass of the catalyst. %to be.

It is preferable that the catalyst for exhaust gas treatment of this invention contains sulfur (S). As a method for addition of sulfur, for example, it may be used by appropriately selected from a method of immersing the catalyst in the aqueous solution such as an aqueous solution of sulfuric acid or a sulfate, sulfur dioxide, a catalytic method for contacting a gas containing (SO ₂₎ or the like.

As a sulfur source, sulfuric acid, ammonium sulfate, ammonium hydrogen sulfate, sulfur dioxide gas, etc. can be selected suitably, for example.

When the catalyst for exhaust gas treatment of this invention contains sulfur, the content is 0.01-3 mass% with respect to the gross mass of a catalyst, Preferably it is 0.1-3 mass%, More preferably, it is 0.5-3 mass%.

As the catalyst for exhaust gas treatment according to the present invention, only the titanium oxide and vanadium, tungsten, and / or molybdenum (hereinafter, collectively referred to as a catalyst component) are used as a constituent material of the catalyst, and the catalyst component is used in a constant shape. Although the shaping | molding catalyst formed by shaping | molding is a preferable form, the supported catalyst formed by carrying a catalyst component in arbitrary inert support | carriers which have a desired shape, or the catalyst obtained by combining suitably the said shaping | molding catalyst and a supported catalyst may be sufficient.

There is no restriction | limiting in particular about the shape of the catalyst for waste gas treatment of this invention, The shape generally used for this kind of catalyst, for example, honeycomb form, spherical shape, plate shape, network shape, columnar shape, cylindrical shape, wave shape (coro Gate) shape, pipe shape, donut shape and the like can be appropriately selected.

The pore volume of the catalyst for exhaust gas treatment of the present invention is usually 0.2 to 0.8 cm 3 / g, preferably 0.25 to 0.7 cm 3 / g, more preferably 0.25 to 0.6 cm 3 / g.

The BET specific surface area of the catalyst for exhaust gas treatment of the present invention is not particularly limited, but is preferably 30 to 250 m 2 / g, more preferably 40 to 250 m 2 / g, still more preferably 45 to 250 M 2 / g.

The exhaust gas containing the harmful substances, such as nitrogen oxides and dioxins, is made to contact the waste gas processing catalyst of this invention as mentioned above, and a hazardous substance can be decomposed and an exhaust gas can be processed. There is no restriction | limiting in particular about a contact condition, It can carry out under the conditions generally used for this kind of process. The space velocity of the exhaust gas is usually 100 to 100,000 ^{hr -1} (STP), preferably 200 to 50,000 ^{hr -1} (STP), and more preferably 200 to 29,000 hr ^-1 (STP). Regarding the treatment temperature, the temperature of the exhaust gas to be treated is usually 100 to 500 ° C, preferably 200 to 500 ° C, more preferably 250 to 500 ° C.

The present invention will be described more specifically with reference to the following examples which show advantageous embodiments of the present invention.

(Example 1)

<Ti-Si composite oxide (a)>

10 kg of Snowtex-20 (manufactured by Nissan Chemical Co., Ltd., containing about 20% by weight of SiO ₂ ) was added to 137 liters of 25 mass% ammonia water, and stirred and mixed, followed by 70 g / liter of titanium sulfate sulfate solution (TiO ₂ , Sulfuric acid concentration 287 g / liter) 257 liters was dripped over 120 minutes (pH8), stirring. After leaving the obtained gel for 20 hours, it filtered, washed with water, and then dried at 120 degreeC for 20 hours. This was calcined at 500 DEG C for 5 hours, further ground using a hammer mill, and classified into a classifier to obtain a powder having an average particle diameter of 12 mu m.

The X-ray diffraction diagram of the obtained powder is shown in FIG. Clear inherent peaks of SiO ₂ did not appear, and wide diffraction peaks were obtained at 2θ = 25.3 °, and it was confirmed that the powder was a composite oxide of titanium and silicon (Ti-Si composite oxide) (a).

Honeycomb Catalyst

1.3 kg of ammonium metavanadate, 1.9 kg of ammonium paratungstate, 2.0 kg of oxalic acid, and 1.2 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. First, 18.0 kg of the prepared Ti-Si composite oxide (a) powder was added to a kneader, and then the homogeneous solution was added with a molding aid such as an organic binder (1.5 kg of starch) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader, and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (1). The composition of this catalyst was Ti: Si: V: W (conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : WO ₃ ) = 78.3: 8.7: 5: 8.

About the catalyst (1), the chart calculated | required by the FT-IR analysis method is shown in FIG. 2, and the ratio (B / L) calculated | required based on this chart is shown in Table 1. FIG.

(Example 2)

In Example 1, the catalyst (2) was similarly obtained except having used 2.0 kg of ammonium paramolybdates instead of 1.9 kg of ammonium paratungstates. The composition of this catalyst (2) was Ti: Si: V: Mo (the conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : MoO ₃ ) = 78.3: 8.7: 5: 8. Table 1 shows the ratio (B / L) determined by the FT-IR analysis of the catalyst (2).

<Ti-Si-Mo composite oxide (b)>

(Example 3)

3.4 kg of molybdate is added to a mixed solution of 3.3 kg of silica sol (Snowtex-30, manufactured by Nissan Chemical Co., Ltd., 30 mass% in terms of SiO ₂ ), 103 kg of industrial ammonia water (containing 25 mass% ammonia) and 58 liters of water. By stirring, molybdic acid was completely dissolved to obtain a homogeneous solution. 228 liters of a sulfuric acid solution of titanium sulfate (70 g / liter as TiO ₂ , sulfuric acid concentration 287 g / liter) was added dropwise to the solution over 120 minutes with stirring to precipitate (pH8). This coprecipitation slurry was left to stand for about 40 hours, and it filtered, and after wash | cleaning enough with water, it dried at 100 degreeC for 1 hour. Moreover, it baked at 500 degreeC in air atmosphere for 5 hours. It was pulverized using a hammer mill and classified with a classifier to obtain a powder having an average particle diameter of 12 µm.

In the X-ray diffraction chart of the obtained powder, no clear inherent peaks of SiO ₂ and MoO ₃ were found, and a broad diffraction peak was obtained at 2θ = 25.3 °, thereby obtaining a composite oxide of titanium, silicon, and molybdenum (Ti-Si-Mo composite oxide). (b) was confirmed.

Honeycomb Catalyst

1.8 kg of ammonium metavanadate, 1.67 kg of oxalic acid, and 0.4 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. First, 18.6 kg of the Ti-Si-Mo composite oxide powder thus prepared was added to a kneader, and then the vanadium-containing solution was added with a molding aid such as an organic binder (1.5 kg of starch) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader, and extruded into a honeycomb phase having an outer shape of 80 mm, an eye size of 44.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (3). The composition of this catalyst was Ti: Si: Mo: V (conversion ratio of TiO ₂ : SiO ₂ : MoO ₃ : V ₂ O ₅ ) = 74.3: 4.7: 14: 7. Table 1 shows the ratio (B / L) determined by the FT-IR analysis of the catalyst (3).

(Example 4)

1.8 kg of ammonium metavanadate, 1.7 kg of ammonium sulfate, 1.67 kg of oxalic acid, and 0.4 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. 6.2 kg of commercially available TiO ₂ powder (DT-51 (trade name), manufactured by Millennium) was added to the kneader, and the vanadium-containing solution was added with a molding aid such as an organic binder (1.5 kg of starch) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (4). The composition of this catalyst was Ti: V: S (conversion ratio of TiO ₂ : V ₂ O ₅ : S) = 92.5: 7: 0.5. Ratio (B /) obtained by FT-IR analysis of the catalyst (4) L) is shown in Table 1.

(Comparative Example 1)

<Ti-Si complex oxide (d)>

10 kg of Snowtex-20 was added to 257 liters of a sulfuric acid solution of titanium sulfate (70 g / liter as TiO ₂ , sulfuric acid concentration 287 g / liter), stirred and mixed, and the mixed aqueous solution was heated to 70 ° C. 137 liters of 25 mass% ammonia water was added dropwise to the heated mixed aqueous solution over 30 minutes with stirring, and then adjusted to pH = 7. After stirring the obtained gel for 2 hours at 70 degreeC, it filtered and washed with water and then dried at 100 degreeC for 20 hours. This was calcined at 500 DEG C for 5 hours, further ground using a hammer mill, and classified into a classifier to obtain a powder having an average particle diameter of 12 mu m.

The X-ray diffraction diagram of the obtained powder is shown in FIG. According to this, a clear inherent peak of SiO ₂ did not appear, and a wide diffraction peak was obtained at 2θ = 25.3 °, and it was confirmed that the powder was a composite oxide (Ti-Si composite oxide) (d) of titanium and silicon.

Honeycomb Catalyst

1.3 kg of ammonium metavanadate, 1.9 kg of ammonium paratungstate, 2.0 kg of oxalic acid, and 1.2 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. First, 18 kg of the prepared Ti-Si composite oxide (d) was added to the kneader, and then the vanadium and tungsten-containing solution were added together with the molding aid of the organic binder (starch 1.5 kg) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it calcined at 450 degreeC for 5 hours, and obtained the catalyst (5). The composition of this catalyst 5 was Ti: Si: V: W (conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : WO ₃ ) = 78.3: 8.7: 5: 8. About the catalyst 5, the chart calculated | required by the FT-IR analysis method is shown in FIG. 4, and the ratio (B / L) calculated | required based on this chart is shown in Table 1. FIG.

(Comparative Example 2)

Commercially available V ₂ O ₅ 1.4 kg of powder is mixed with 18.6 kg of anatase-type titanium oxide powder (DT-51 (trade name), manufactured by Millennium Co., Ltd.), added to a kneader, and a suitable amount of water is added together with a molding aid such as an organic binder (1.5 kg of starch). After mixing well with a blender, it knead | mixed sufficiently by the continuous kneader, and extruded into the honeycomb shape of the external shape of 80 mm, eye size 4.0 mm, thickness 1.0 mm, and length 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 500 degreeC for 5 hours, and obtained the catalyst (6). The composition of this catalyst was Ti: V = 95: 5 (a conversion ratio in terms of TiO ₂ : V ₂ O ₅ ).

The X-ray diffraction diagram of the anatase-type titania oxide powder is shown in Fig. 5. A ratio (B / L) determined by the FT-IR analysis of the catalyst (6) is shown in Table 1.

(Example 5)

Using the catalysts (1) to (6) obtained in Examples 1 to 4 and Comparative Examples 1 to 2, an activity evaluation test (denitration reaction test and chlorotoluene decomposition test) was carried out under the following conditions.

(Activity Evaluation Test)

36.3 ml of each of the catalysts (1) to (6) were filled in a stainless steel reaction tube having a length of 1200 mm and a diameter of 50 mm, and the following reaction gas was allowed to flow at the reaction gas temperature and space velocity shown below. The NOx removal rate (denitrification rate) and the chlorotoluene decomposition rate were determined by measuring the concentration and the chlorotoluene concentration.

(Denitration test conditions)

Reaction gas = NOx: 200ppm, NH ₃ : 200ppm, SO ₂ : 50ppm, O ₂ : 10%, H ₂ O: 12%, N ₂ : Balance

Reaction gas temperature: 200 ℃, 300 ℃ and 400 ℃

Space Speed: 17,000hr ^-1 (STP)

Denitrification was calculated | required according to the following formula.

Denitrification Rate = [(Reactor Inlet NOx Concentration)-(Reactor Outlet NOx Concentration)] ÷ (Reactor Inlet NOx Concentration) × 100

(Chlorotoluene Degradation Test Conditions)

Reaction gas = chlorotoluene: 20 ppm, SO ₂ : 50 ppm, O ₂ : 10%, H ₂ O: 12%, N ₂ : Balance

Reaction gas temperature: 200 ℃

Space Speed: 3800hr ^-1

Chlorotoluene decomposition rate was calculated | required according to the following formula.

Chlorotoluene decomposition rate = [(Reactor inlet chlorotoluene concentration)-(Reactor outlet chlorotoluene concentration)] ÷ (Reactor inlet chlorotoluene concentration) × 100

The results are shown in Table 1.

(Example 6)

In Example 1, the amount of 25 mass% ammonia water was changed to 69 liters, except that 88 liters of an aqueous titanium tetrachloride solution (containing 36 mass% as TiO ₂ ) was used instead of 257 liters of sulfuric acid solution of titanium sulfate. And Ti-Si composite oxide (e) were obtained. About the obtained Ti-Si composite oxide (e), the ratio obtained by the FT-IR analysis method in Table 1 for the amount of solid acids whose pKa <= + 3.3 is shown in FIG. 6, and was calculated | required based on this chart (B / L ) Is shown in Table 2.

Honeycomb Catalyst

1.3 kg of ammonium metavanadate, 1.9 kg of ammonium paratungstate, 2.0 kg of oxalic acid, and 1.2 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. First, 18 kg of the prepared Ti-Si composite oxide (e) powder was added to a kneader, and then the homogeneous solution was added with a molding aid such as an organic binder (1.5 kg of starch) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (1). The composition of this catalyst was Ti: Si: V: W (conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : WO ₃ ) = 78.3: 8.7: 5: 8.

(Example 7)

In Example 6, the catalyst (8) was obtained similarly except having used 2.0 kg of ammonium paramolybdates instead of 1.9 kg of ammonium paratungstates at the time of preparation of a honeycomb catalyst. The composition of this catalyst (8) was Ti: Si: V: Mo (the conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : MoO ₃ ) = 78.3: 8.7: 5: 8.

(Example 8)

In Example 3, the amount of ammonia water was changed to 52 kg, and Ti-Si was similarly used except that 78 liters of titanium tetrachloride aqueous solution (containing 36 mass% as TiO ₂ ) was used instead of 228 liters of sulfuric acid solution of titanium sulfate. -Mo composite oxide (f) was obtained. About the obtained Ti-Si-Mo composite oxide (f), the ratio (B / L) calculated | required by Table 2 and the FT-IR analysis method for the solid acid amount which pKa <= 3.3 is shown in Table 2.

Honeycomb Catalyst

In 8 liters of water, 1.29 kg of ammonium metavanadate, 1.67 kg of oxalic acid, and 0.4 kg of monoethanolamine were mixed and dissolved to prepare a homogeneous solution. First, 19 kg of the prepared Ti-Si-Mo composite oxide (f) powder was added to a kneader, and then the vanadium-containing solution was added with a molding aid such as an organic binder (1.5 kg of starch) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (3). The composition of this catalyst was Ti: Si: Mo: V (conversion ratio of TiO ₂ : SiO ₂ : MoO ₃ : V ₂ O ₅ ) = 76.4: 4.8: 14.2: 5.

(Example 9)

<TiO ₂ powder (g)>

To 160 liters of 25 mass% ammonia water, 300 liters of a titanium sulfate solution (70 g / liter as TiO ₂ , sulfuric acid concentration 287 g / liter) was added dropwise over 120 minutes with stirring (pH 8). After leaving the obtained gel for 20 hours, it filtered, washed with water, and then dried at 120 degreeC for 20 hours. This was calcined at 520 ° C. for 3 hours, ground using a hammer mill, and classified with a classifier to obtain TiO ₂ powder (g) having an average particle diameter of 12 μm.

The solid acid amount, pKa≤ + 3.3 with respect to the TiO ₂ powder (g) in Table 2, also showed a ratio (B / L) as determined by FT-IR analysis are shown in Table 2.

Honeycomb Catalyst

Example according to 8, Ti-Si-Mo composite oxide (f) instead of the same manner as in Example 8 except that the powdery TiO ₂ (g) to obtain a catalyst (10). The composition of this catalyst (10), Ti: V (TiO _2: ratio converted to V ₂ O ₅₎ = 95: 5 was.

(Comparative Example 3)

In Comparative Example 1, the amount of ammonia water was changed to 69 kg, and Ti-Si was similarly used except that 88 liters of an aqueous titanium tetrachloride solution (containing 36 mass% as TiO ₂ ) was used instead of 257 liters of sulfuric acid solution of titanium sulfate. Composite oxide (h) was obtained. About the obtained Ti-Si composite oxide (h), the chart obtained by Table 2 and the FT-IR analysis method for the solid acid amount of pKa <= 3.3 is shown in FIG. 7, and the ratio (B / L) calculated | required based on this chart ) Is shown in Table 2.

Honeycomb Catalyst

1.3 kg of ammonium metavanadate, 1.9 kg of ammonium paratungstate, 2.0 kg of oxalic acid, and 1.2 kg of monoethanolamine were mixed and dissolved in 8 liters of water to prepare a homogeneous solution. First, 18 kg of the prepared Ti-Si composite oxide (h) was added to the kneader, and then the vanadium and tungsten-containing solution were added together with the molding aid of the organic binder (starch 1.5 kg) and stirred well. The mixture was mixed well with a blender while adding an appropriate amount of water, and then sufficiently kneaded in a continuous kneader and extruded into a honeycomb phase having an external shape of 80 mm, an eye size of 4.0 mm, a thickness of 1.0 mm, and a length of 500 mm. After drying the obtained molded object at 60 degreeC, it baked at 450 degreeC for 5 hours, and obtained the catalyst (11). The composition of this catalyst was Ti: Si: V: W (conversion ratio of TiO ₂ : SiO ₂ : V ₂ O ₅ : WO ₃ ) = 78.3: 8.7: 5: 8.

(Comparative Example 4)

<TiO ₂ powder (i)>

In Example 9, when preparing the TiO ₂ powder (g), the gel was filtered and then washed with water, and then dried at 120 ° C. for 20 hours as it is. This was calcined at 520 ° C. for 3 hours, further ground using a hammer mill, and classified by a classifier to obtain TiO ₂ powder (i) having an average particle diameter of 12 μm.

The solid acid amount, pKa≤ + 3.3 with respect to the powder TiO ₂ (i) are shown in Table 2, and showed a ratio (B / L) as determined by FT-IR analysis are shown in Table 2.

In the following Example 9, a honeycomb catalyst was prepared in the same manner as in Example 9 except that TiO ₂ powder (i) was used instead of TiO ₂ powder (g) to obtain a catalyst (12). The composition of this catalyst was Ti: V: S = 85: 5: 10 (conversion ratio to TiO ₂ : V ₂ O ₅ : S).

(Example 10)

Using the catalysts (7) to (12) obtained in Examples 6 to 9 and Comparative Examples 3 to 4, an activity evaluation test (denitration reaction test and chlorotoluene decomposition test) was carried out under the following conditions.

(Activity Evaluation Test)

Using the catalysts (7) to (12), NOx removal rate (denitrification rate) and chlorotoluene decomposition rate were determined in the same manner as in Example 5.

(Denitration reaction conditions)

Reaction gas = NOx: 200ppm, NH ₃ : 200ppm, SO ₂ : 50ppm, O ₂ : 9%, H ₂ O: 15%, N ₂ : Balance

Reaction gas temperature: 200 ℃, 300 ℃ and 400 ℃

Space Speed: 15,000hr ^-1 (STP)

Denitrification was calculated | required according to the following formula.

Denitrification Rate = [(Reactor Inlet NOx Concentration)-(Reactor Outlet NOx Concentration)] ÷ (Reactor Inlet NOx Concentration) × 100

(Chlorotoluene Degradation Test Conditions)

Reaction gas = chlorotoluene: 40 ppm, SO ₂ : 50 ppm, O ₂ : 9%, H ₂ O: 15%, N ₂ : Balance

Reaction gas temperature: 200 ℃

Space Speed: 3100hr ^-1

Chlorotoluene decomposition rate was calculated | required according to the following formula.

Chlorotoluene decomposition rate = [(Reactor inlet chlorotoluene concentration)-(Reactor outlet chlorotoluene concentration)] ÷ (Reactor inlet chlorotoluene concentration) × 100

The results are shown in Table 2.

(Example 11)

In Example 1, Ti-Si composite oxide (j) and the catalyst (13) were obtained like Example 1 except having added the sulfuric acid solution of titanium sulfate over 90 minutes. The ratio (B / L) determined by the FT-IR method of the catalyst 13 is shown in Table 3, and the amount of solid acid having a pKa? The ratio (B / L) determined by the above is shown in Table 4, respectively.

(Example 12)

In Example 1, Ti-Si composite oxide (k) and catalyst (14) were obtained like Example 1 except having added the sulfuric acid solution of titanyl sulfate over 60 minutes. The ratio (B / L) determined by the FT-IR method of the catalyst 14 is shown in Table 3, and the amount of solid acid having a pKa? The ratio (B / L) determined by the above is shown in Table 4, respectively.

(Example 13)

In Example 1, except that 137 liters of 25 mass% aqueous ammonia water and 10 kg of Snowtex-20 were added dropwise to 257 liters of sulfuric acid solution of titanyl sulfate over stirring for 120 minutes in the same manner as in Example 1 Si composite oxide (1) and catalyst (15) were obtained. The ratio (B / L) obtained by the FT-IR method of the catalyst 15 is shown in Table 3, and the amount of solid acid having a pKa ≤ +3.3 for Ti-Si composite oxide (l) is shown in Table 4, and the FT-IR method. The ratio (B / L) determined by the above is shown in Table 4, respectively.

(Example 14)

Using the catalysts (1), (13), (14), (15) and (5) obtained in Examples 1, 11, 12, 13 and Comparative Example 1, the activity evaluation tests were carried out under the same conditions as in Example 5. It was done. The results are shown in Table 3.

(Example 15)

Using the catalysts (7), (13), (14), (15) and (11) obtained in Examples 6, 11, 12, 13 and Comparative Example 3, the activity evaluation tests were carried out under the same conditions as in Example 10. It was done. The results are shown in Table 3.

By using the catalyst of the present invention, harmful substances such as nitrogen oxides and dioxins can be efficiently decomposed and removed.

Claims (18)

An exhaust gas treating catalyst for decomposing and removing harmful substances in exhaust gas containing titanium oxide and other catalytically active ingredients, The molar ratio (B / L) of Bronsted acid (B) and Lewis acid (L) is in the range of 0.1 / 1 to 10/1, The titanium oxide is titanium oxide; Or a composite oxide of titanium with at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten, The other catalytically active component is at least one element selected from the group consisting of vanadium, tungsten and molybdenum or a compound thereof, The content of the titanium oxide is 75 to 99.9% by mass based on the total amount of the catalyst, and the content of the other catalytically active components is 0.1 to 25% by mass based on the total amount of the catalyst. . The method of claim 1, The catalyst is characterized in that the ratio is 0.1 / 1 to 9/1. delete delete The method of claim 1, And the titanium oxide is a composite oxide of titanium with at least one element selected from the group consisting of aluminum, silicon, chromium and zirconium. The method of claim 1, And the titanium oxide is a complex oxide of titanium with at least one element selected from the group consisting of aluminum, silicon and zirconium. delete The method of claim 1, In the case where the titanium oxide is a titanium composite oxide, the titanium content in the titanium composite oxide is 40 to 95 mass% with respect to the total mass of titanium and other elements of the titanium composite oxide, and the other catalytically active component The catalyst is 5 to 60 mass% with respect to the total mass of the said titanium and the said other element (however, the sum total of the said titanium complex oxide and another catalytically active component is 100 mass%). delete The method of claim 1, A catalyst comprising further sulfur. The method of claim 1, And said ratio (B / L) of said titanium oxide is 0.1 / 1 to 1/1, and the amount of solid acid having a pKa &lt; +3.3 is 0.3 mmol / g or more. The method of claim 11, A catalyst characterized in that the amount of solid acid having a pKa ≤ +3.3 is 0.3 ~ 0.8 mmol / g. The method of claim 10, The sulfur content is 0.01 to 3% by mass relative to the total mass of the catalyst. In the acid solution containing the titanium compound, an aqueous solution of ammonia containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten is added to form a precipitate. A method for producing a catalyst according to claim 1, wherein the titanium composite oxide obtained through the step of adding the total amount to 40 minutes to 1440 minutes is used. In the aqueous ammonia solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten, an acidic solution containing a titanium compound is added to form a precipitate. The method for producing a catalyst according to claim 1, wherein the titanium composite oxide obtained through the step of adding the total amount to 40 minutes to 1440 minutes is then used. In an acidic solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum and tungsten and a titanium compound, an aqueous solution of ammonia is added to generate a precipitate. A method for producing a catalyst according to claim 1, wherein the titanium composite oxide obtained through the step of adding a total amount to 40 minutes to 1440 minutes is used. In the aqueous ammonia solution, an acid solution containing at least one element selected from the group consisting of aluminum, silicon, chromium, zirconium, molybdenum, and tungsten and a titanium compound is added to form a precipitate. A method for producing a catalyst according to claim 1, wherein the titanium composite oxide obtained through the step of adding a total amount to 40 minutes to 1440 minutes is used. Exhaust gas containing harmful substances is brought into contact with the catalyst for treating exhaust gas according to any one of claims 1, 2, 5, 6, 8, or 10 to 13. A method for treating exhaust gas, characterized by decomposing and removing harmful substances.

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