JPS6214336B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst for removing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas discharged from fixed combustion equipment of various factories including boilers, thermal power plants, steel mills, etc. In particular, the present invention
and sulfur compounds (mainly sulfur dioxide or SOx
shall be. ), ammonia is added as a reducing agent to the exhaust gas and reacted catalytically, which efficiently decomposes NOx into harmless nitrogen and water, and at the same time converts the generated sulfur dioxide (SO ₂ ) into sulfur trioxide (SO ₃ ). The purpose of the present invention is to provide a catalyst that suppresses the oxidation reaction of oxidation reactions to a low level and has excellent durability. Methods for removing NOx from exhaust gas can be broadly classified into adsorption methods, absorption methods, and catalytic reduction methods, but among these methods, catalytic reduction methods have a large amount of exhaust gas to process and do not require wastewater treatment, so they are technically and economically preferable. is also advantageous. Catalytic reduction methods include a non-selective reduction method using a hydrocarbon such as methane, LPG, hydrogen, or carbon monoxide as a reducing agent, and a selective reduction method using ammonia as a reducing agent. In the latter case, NOx can be selectively removed even from exhaust gas containing a high concentration of oxygen, and since only a small amount of reducing agent is required, it is economical and extremely advantageous. The first characteristic that a catalyst must have in a selective catalytic reduction method using ammonia as a reducing agent is that exhaust gas contains oxygen, SOx, carbon dioxide, water vapor, halogen compounds, hydrocarbons, etc. be unaffected by coexisting gases. Second, it must exhibit sufficient performance over a wide temperature range and at high space velocities. Third, the soot and dust present in the exhaust gas contains heavy metals such as vanadium, nickel, and iron, as well as alkali metals such as sodium and potassium, but even if these soot and dust adhere, the catalyst will not be covered. Don't be poisoned. Fourth, the ability to oxidize sulfur dioxide (SO ₂ ) into sulfur trioxide (SO ₃ ) in exhaust gas is small. In other words, SO ₂ contained in the exhaust gas is oxidized on the catalyst and becomes SO ₃ , which accumulates on the catalyst and reduces the denitrification activity, and also reacts with ammonia added as a reducing agent to form ammonium sulfate and acid. There are drawbacks such as the generation of ammonium sulfate, which accumulates and blocks equipment such as flues and heat exchangers, impeding smooth operation. Therefore, as much as possible
A catalyst that suppresses the oxidation of SO ₂ to SO ₃ is desired. The above four points are important characteristics that a catalyst should have. The present inventors have already disclosed a catalyst that has high denitrification activity, good durability, and low SO ₂ oxidation activity (for example, see Japanese Patent Application Laid-Open No. 122293/1983). We learned that when dealing with exhaust gas containing a large amount of SO ₂ , a catalyst with even lower SO ₂ oxidation activity is required. According to studies conducted by the present inventors, vanadium oxide in the catalyst provides excellent denitrification activity. On the other hand, it is a major cause of increasing _SO2 oxidation activity. Therefore, although it is possible to suppress SO ₂ oxidation ability by reducing vanadium oxide, the reality is that the denitrification activity must also be reduced at the same time. Therefore, we investigated various preparation methods that would not reduce the denitrification activity even if the vanadium oxide content in the catalyst was reduced. In view of the above points, the present inventors added ammonia to the exhaust gas to remove the coexisting SOx and halogen compounds.
We are developing a durable catalyst that efficiently reduces and removes NOx to harmless nitrogen at high space velocities without being affected by soot and dust, and at the same time has an extremely low ability to oxidize SO ₂ to SO ₃ . As a result,
A binary composite oxide consisting of titanium and silicon, a binary composite oxide consisting of titanium and zirconium, and titanium, silicon,
A catalyst obtained by supporting vanadium, tungsten, and tin in a highly dispersed state using a ternary composite oxide consisting of zirconium and zirconium overcomes the above drawbacks and has excellent long-term performance.
We have completed the catalyst of the present invention by discovering that it maintains NOx removal ability and causes fewer operational troubles. That is, the present invention can be specified as follows. (1) As a catalyst that selectively reduces nitrogen oxides in exhaust gas by catalytically reacting them with ammonia,
Using a soluble titanium compound as a titanium source, a soluble zirconium compound as a zirconium source, and a soluble silicon compound and/or silica sol as a silicon source, a coprecipitate is obtained by a neutralization reaction, which is washed, dried, and fired. At least one member selected from the group consisting of a binary composite oxide of titanium and silicon, a binary composite oxide of titanium and zirconium, and a ternary composite oxide of titanium, silicon, and zirconium. composite oxide as catalyst A component, vanadium oxide as catalyst B component, and tungsten oxide as catalyst C component.
and tin oxide and/or tin sulfate as the catalyst component D, the composition of which is 73 to 95% by weight for A, 0.3 to 3% by weight for B, and 0.3 to 3% by weight for C.
is in the range of 3 to 12% by weight, D is in the range of 0.5 to 10% by weight, tin/tungsten is in the range of 0.1 to 3.0 in atomic ratio, and the composition of component A is 40 to 95% titanium oxide in mole percent as oxide. , silicon and/or zirconium oxide in a range of 5 to 60%. The first feature of the catalyst of the present invention is that it is a binary composite oxide consisting of titanium and silicon (hereinafter referred to as TiO ₂ -SiO ₂ ) and a binary composite oxide consisting of titanium and zirconium (hereinafter referred to as TiO ₂ -ZrO _{2 )} . ) and a ternary composite oxide (hereinafter referred to as TiO ₂ -ZrO ₂ -SiO ₂ ) consisting of titanium, zirconium and silicon. _TiO2 − _SiO2 , _TiO2 − _ZrO2 and _TiO2 − _ZrO2−
SiO ₂ itself has activity against _NOx in exhaust gas _, and at the _same time, in the present invention, _it also plays the role of _a carrier _. Physical properties ₂ also provide desirable physical properties to the finished catalyst. TiO ₂ -SiO ₂ in the present invention is known as a solid acid, as is well known, for example, by Kozo Tabe (Catalysts, Vol. 17, No. 3, p. 72 (1975)), and each constituent individual TiO ₂ -SiO ₂ is not a simple mixture of titanium oxide and silicon oxide, but a so-called binary oxide of titanium and silicon. It can be recognized that unique physical properties are expressed by forming a substance. Similarly, TiO ₂ -ZrO ₂ and TiO ₂ -ZrO ₂ -SiO ₂ also have the same physical properties as the above-mentioned TiO ₂ -SiO ₂ . Furthermore, TiO ₂ −SiO ₂ , TiO ₂ −ZrO ₂ and TiO ₂ −ZrO ₂ − used in the present invention
All SiO ₂ was found to be amorphous as a result of X-ray diffraction analysis. _TiO2 − _SiO2 , _TiO2 − _ZrO2 and _TiO2 − _ZrO2−
The advantage of using SiO ₂ is that the catalyst of the present invention exhibits remarkable acid resistance, is completely unaffected by SOx and halogen compounds, and exhibits a stable NOx purification ability over a long period of time. Furthermore, the catalyst of the present invention comprises _TiO2 - _SiO2 , _TiO2 - _ZrO2 and _TiO2 - _ZrO2
- Since SiO ₂ is used, it has the advantage that the ability to oxidize sulfur dioxide (SO ₂ ) present in the processing gas into sulfur trioxide (SO ₃ ) is extremely low. This prevents the dew point temperature from rising due to SO ₃ present in the reduced gas, making it possible to perform heat exchange using a heat exchanger more economically.
This is extremely advantageous industrially in terms of preventing material corrosion due to the generated SO ₃ . In addition, other features are
_TiO2 − _SiO2 , _TiO2 − _ZrO2 and _TiO2 − _ZrO2−
The present catalyst using SiO ₂ exhibits good NOx purification ability over an extremely wide range of temperatures and high space velocities. The second characteristic of the catalyst of the present invention is that the _catalyst components of the present invention are in a highly dispersed state. Another advantage is that unexpectedly high denitrification activity can be obtained. As a result of X-ray diffraction analysis, the catalyst of the present invention is essentially amorphous. No diffraction peaks were observed for vanadium, tungsten, and tin oxides, which are catalytic active components, or sulfates, and component A, TiO ₂ -SiO ₂ , TiO ₂ - has a high surface area.
This is because it interacts with ZrO ₂ and TiO ₂ -ZrO ₂ -SiO ₂ and is highly dispersed. Thus, TiO ₂ −SiO ₂ , TiO ₂ −ZrO ₂ and
When TiO ₂ -ZrO ₂ -SiO ₂ is used as catalyst component A, it works effectively to improve the denitrification activity even if the vanadium content is lowered and tungsten and tin, which have lower denitrification activity than vanadium, are used. On the contrary, it selectively removes SO ₂ without significantly reducing denitrification activity.
It has been discovered that it is possible to obtain a catalyst with significantly reduced oxidation activity and excellent durability. In the catalyst of the present invention, when the content of vanadium as an oxide is 3% by weight or more, the SO ₂ oxidation activity increases, and when the content is 0.3% by weight or less, the denitrification activity is significantly reduced. It has been found that it is preferably between 0.3 and 2.5% by weight. In addition, if the content of tungsten as an oxide is less than 3% by weight, the denitrification activity will be extremely reduced, and if it is more than 12% by weight, the denitrification activity cannot be expected to improve much, and the raw material cost of the catalyst will increase.
It has been found that a range of 12% by weight, preferably between 5 and 11% by weight, is preferred. On the other hand, tin has been found to have the same effect as tungsten, and in particular when used in combination with tungsten, the denitrification activity was dramatically improved, and a synergistic effect was observed. The tin content is 0.5 to 10% by weight as an oxide, preferably 1 to 10% by weight.
It is preferably 7% by weight. In the catalyst of the present invention, a synergistic effect is exhibited when tin is contained in the range of 0.1 to 3.0 (atomic ratio) to tungsten. In particular, the above-mentioned effects are observed when the catalyst is prepared by introducing both the tungsten compound and the tin compound in the form of an aqueous solution. Of course, it is not preferable to deviate from the above range; for example, if it is less than 0.1, the synergistic effect of tin addition will be weakened, and if it is more than 3, the effectiveness of tin-tungsten will not further increase. In the catalyst of the present invention, vanadium,
Tungsten and tin are each supported in an extremely finely dispersed manner, with no peaks visible even in X-ray diffraction, and the dispersed state is maintained even during long-term use, so there is no thermal deterioration due to sintering, etc. , it was recognized that it exhibited excellent heat resistance. By the way, as the vanadium content in the catalyst decreases, TiO ₂ /SiO ₂ , TiO ₂ /ZrO ₂ , and
The influence of the TiO ₂ /(ZrO ₂ +SiO ₂ ) content ratio on the denitrification activity becomes significant. In particular, when vanadium is 3% by weight or less as an oxide, titanium is 40% or less as an oxide, and silicon and/or zirconium is 60% or more, the denitrification activity becomes poor. Also, if titanium is 95% or more and silicon and/or zirconium is 5% or less
This is undesirable as it increases SO ₂ oxidation activity. Therefore,
A preferred range is 40-95% titanium and 5-60% silicon and/or zirconium in mole percentage as oxide. On the other hand, _TiO2 - _SiO2 , _TiO2 - _ZrO2 , and _TiO2 - _ZrO2 were used to improve the dispersion of catalytic active components.
-SiO ₂ has a specific surface area of 80 m ² /g or more, especially 100 m ² /g
The above is preferable. To prepare TiO ₂ -SiO ₂ used in the present invention, first select a titanium source from inorganic titanium compounds such as titanium chlorides and titanium sulfate, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate. The silicon source can be selected from inorganic silicon compounds such as colloidal silica, water glass, silicon tetrachloride, and organic silicon compounds such as tetraethyl silicate. Some of these raw materials contain trace amounts of impurities and contaminants,
This is not a problem unless it greatly affects the physical properties of the TiO ₂ −SiO ₂ obtained. A preferred method for preparing TiO ₂ -SiO ₂ includes the following method. A method in which titanium tetrachloride is mixed with silkasol, ammonia is added to form a precipitate, the precipitate is washed, dried, and then calcined at 300 to 650°C. A method in which a sodium silicate aqueous solution is added to titanium tetrachloride and reacted to form a precipitate, which is then washed and dried and then calcined at 300 to 650°C. A method in which ethyl silicate [(C ₂ H ₅ O) ₄ Si] is added to a water-alcohol solution of titanium tetrachloride to cause a hydrolysis reaction to form a precipitate, which is washed, dried, and then calcined at 300 to 650°C. Ammonia is added to a water-alcohol solution of titanium oxide chloride (TiOCl ₂ ) and ethyl silicate to form a precipitate, which is washed and dried at a temperature of 300 to 650
A method of firing at ℃. Among the above preferred methods, this method is particularly preferred, and this method is specifically carried out as follows. That is, the above-mentioned titanium source and silicon source compounds are taken so that the molar ratio of TiO ₂ and SiO ₂ is a predetermined amount, and titanium and silicon are converted into oxides in an acidic aqueous solution state or sol state to 1 to 1.
Make the concentration 100g/keep at 10-100℃. Aqueous ammonia was added dropwise as a neutralizing agent into the solution while stirring, and a coprecipitated compound consisting of titanium and silicon was produced at pH 2 to 10 for 10 minutes to 3 hours.
After separating and washing well, drying at 80-140°C for 1-10 hours, baking at 300-650°C for 1-10 hours to obtain TiO ₂ −
You can get SiO ₂ . Furthermore, for TiO ₂ −ZrO ₂ −SiO ₂ , TiO ₂ −
It is prepared by a method similar to SiO ₂ , and the zirconium source can be selected from inorganic zirconium compounds such as zirconium chloride and zirconium sulfate, and organic zirconium compounds such as zirconium oxalate. That is, _TiO2 - _ZrO2 - _SiO2 can be easily prepared by treating a zirconium compound together with a titanium compound in the same manner as described above. The amount of zirconium present is preferably within a range of up to 30% by weight in terms of ZrO ₂ based on the total amount of TiO ₂ +ZrO ₂ +SiO ₂ . The method for preparing TiO ₂ -ZrO ₂ can be performed in the same manner. Next, TiO ₂ −SiO ₂ , TiO ₂ −ZrO ₂ and TiO ₂ −
Starting materials for other catalyst components used with ZrO ₂ -SiO ₂ include oxides, hydroxides, ammonium salts,
It is appropriately selected from oxalates, sulfates, halides, etc. Especially when tin is used, tin sulfate gives favorable results. An example of the catalyst preparation method in the present invention is to dissolve ammonium metavanadate and tin sulfate in an aqueous oxalic acid solution, and then add a solution obtained by dissolving ammonium paratungstate together with monoethanolamine. and a solution containing tin. Next, the obtained aqueous solution was added to the aqueous solution obtained by the above method.
TiO ₂ -SiO ₂ powder is added together with a molding aid, mixed and kneaded, and molded into a honeycomb shape using an extrusion molding machine. After drying the molded product at 50-120℃, 300-650℃,
The catalyst can be obtained by calcining preferably at 350-550° C. for 1-10 hours, preferably 2-6 hours in a stream of air. Alternatively, it is also possible to adopt a method in which TiO ₂ -SiO ₂ powder is formed into a honeycomb shape in advance, and the honeycomb is impregnated with an aqueous solution containing vanadium, tungsten, and tin to support the honeycomb. It is also possible to use additional carriers. Examples of carriers include alumina, silica, silica alumina, bentonite,
Diatomaceous earth, silicon carbide, titania, zirconia, magnesia, cordierite, mullite, pumice, activated carbon, inorganic fibers, etc. can be used, for example, granular silicon carbide with TiO ₂
- It can be prepared by making a slurry of SiO ₂ and other catalyst components and supporting it by an impregnation method. Of course, the catalyst preparation method is not limited to these methods. The catalyst shape is not limited to the above-mentioned honeycomb shape, but also cylindrical, cylindrical, plate, ribbon, corrugated, etc.
A pipe shape, a donut shape, a lattice shape, and other integrally molded shapes are appropriately selected. The composition of the exhaust gas to be treated using the catalyst of the present invention is usually 10 to 1500 ppm SOx, 1 to 20% by volume of oxygen, 1 to 15% by volume of carbon dioxide, 5 to 15% by volume of water vapor, and 0.01 to 30 g of soot and dust. / ^Nm3 and NOx
(mainly NO) contained in the range of 100 to 1000 ppm. Normal boiler exhaust gas falls within this range, but the gas composition is not particularly limited. This is because the catalyst of the present invention can also treat special exhaust gases such as NOx-containing exhaust gas that does not contain SOx and NOx-containing exhaust gas that contains halogen compounds. The processing conditions vary depending on the type and properties of the exhaust gas, but the amount of ammonia (NH ₃ ) added is preferably 0.5 to 3 parts per 1 part of NOx. For example, in the exhaust gas composition of a boiler, most of the NOx is NO, so the molar ratio of NO and NH ₃ is 1:1.
Particularly preferred is the vicinity of . This is because care must be taken so that excess NH ₃ is not discharged as an unreacted component. Furthermore, when it is necessary to suppress unreacted NH ₃ as much as possible, it is preferable to use a molar ratio of NH ₃ /NO of 1 or less. Next, the reaction temperature is
150-500℃, especially 200-400℃, space velocity is 1000-100000hr ^-1 , especially 3000-30000hr ^-1
A range of is suitable. There is no particular limit to the pressure
A range of 0.01 to 10 Kg/cm ² is preferred. The type of reactor is not particularly limited, but common fixed bed, moving bed, fluidized bed, and other reactors can be used. The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited only to these Examples. Example 1 _TiO2 - _SiO2 was prepared by the method described below. 114.0 kg of titanium tetrachloride (TiCl ₄ ) was gradually added dropwise to 800 g of water while stirring on ice, and then
(20-21% by weight as silica sol _SiO2 manufactured by Nissan Chemical
(Contains) 45.0Kg was added. Aqueous ammonia was gradually added dropwise to the mixture while stirring the mixture at a temperature of about 30° C. until the pH reached 7, and the mixture was left to mature for 2 hours. The thus obtained TiO ₂ −SiO ₂ gel was filtered, washed with water, dried at 120°C for 10 hours, further washed with water, and then dried at 550°C.
It was baked at ℃ for 3 hours. The composition of the obtained powder was TiO ₂ /SiO ₂ =4 (molar ratio) as an oxide, and the BET surface area was 200 m ² /g. The powder obtained here is hereinafter referred to as TS-1. 0.478 kg of ammonium metavanadate was dissolved in 3 parts of water along with an equal amount of oxalic acid, and then 0.795 kg of stannous sulfate was added and dissolved. This solution and 1.95 kg of ammonium paratungstate were dissolved together with an appropriate amount of monoethanolamine, and the resulting solution 3 was mixed to obtain a homogeneous solution containing vanadium, tungsten, and tin. Furthermore, this solution was added to the above TS-1 16.0Kg, and mixed well with a kneader while adding an appropriate amount of water.
It was molded into a honeycomb with a diameter of 4.6 mm, a wall thickness of 1.3 mm, and a length of 500 mm. Next, after drying this molded product at 50 to 120℃,
It was baked at ℃ for 5 hours under air circulation. The composition of the obtained finished catalyst was TS-1:
WO ₃ :SnO ₂ :V ₂ O ₅ =86:9:3:2. Example 2 TiO ₂ ·SiO ₂ was prepared according to Example 1, except that a sulfuric acid solution of titanyl sulfate containing 55.1 kg of TiO ₂ and 3.0 kg of Snowtex-O were used.
The composition of the obtained powder is TiO ₂ /SiO ₂ as an oxide.
=9 (molar ratio) and the BET surface area was 190 m ² /g. The obtained powder is called TS-2, and this TS-2
A catalyst of the same composition (TS-2:WO ₃ :SnO ₂ :V ₂ O ₅ =86:9:3:2) was prepared in the same manner as in Example 1 using
weight ratio) was prepared. Example 3 Titanium tetrachloride 114.0Kg, zirconium acid chloride [ZrOCl ₂ 8H ₂ O] 12.0Kg and snowtex
TiO ₂ − according to Example 1 except that O34.0Kg was used.
_ZrO2 - _SiO2 was prepared. The composition of the obtained powder was TiO ₂ :ZrO ₂ :SiO ₂ =80:5:15 as an oxide.
(molar ratio), the BET surface area was 210 m ² /g.
The obtained powder is called TZS-1, and using this TZS-1, a catalyst with the same composition (TZS-1: _WO3 : _SnO2 : _V2O5 = ₈₆ :9) was prepared in the same manner as in Example 1. :3:
2 weight ratio) was prepared. Example 4 TiO ₂ -ZrO ₂ was prepared according to Example 1 using titanium tetrachloride and zirconium acid chloride. The composition of the obtained powder is TiO ₂ :ZrO ₂ = 85:15 (molar ratio)
The BET surface area was 170 m ² /g. The obtained powder is called TZ-1, and using this TZ-1, a catalyst with the same composition (TZ-1:
WO ₃ :SnO ₂ :V ₂ O ₅ =86:9:3:2 weight ratio) was prepared. Examples 5 to 8 Example 2 except that the molar ratio of TiO ₂ /SiO ₂ was changed.
TiO ₂ -SiO ₂ was prepared according to . Table 1 shows the composition and BET surface area of the obtained powder. these
A catalyst having the same composition as in Example 1 was prepared using TiO ₂ -SiO ₂ .

[Table] Comparative Example 1 According to Example 2 TiO ₂ /SiO ₂ = 24 (molar ratio)
Prepare TiO ₂ −SiO ₂ powder so that
The BET surface area was 140 m ² /g. Using this powder, a catalyst having a similar composition was prepared in the same manner as in Example 1. Comparative Example 2 TiO ₂ /SiO ₂ = 0.2 (molar ratio) according to Example 2
Prepare TiO ₂ −SiO ₂ powder so that
The BET surface area was 200 m ² /g. Using this powder, a catalyst having a similar composition was prepared in the same manner as in Example 1. Comparative Example 3 _TiO2 - _ZrO2 - _SiO2 was prepared according to Example 3. The composition of the obtained powder is _TiO2 as oxide:
ZrO ₂ :SiO ₂ = 30:60:10 (molar ratio),
The BET surface area was 150 m ² /g. The obtained powder is called TZS-2, and using this TZS-2, a catalyst with the same composition (TZS-2:
WO ₃ :SnO ₂ :V ₂ O ₅ =86:9:3:2 weight ratio) was prepared. Comparative Examples 4-5 TiO ₂ -SiO ₂ powder obtained in Example 1 (TS-
A catalyst containing vanadium, tin and tungsten was prepared according to Example 1 using 1). The composition of the obtained catalyst is as follows. Composition (weight ratio) Comparative example 4 TS-1:WO ₃ :SnO ₂ :V ₂ O ₅ =97.5:2:0.3:0.2 Comparative example 5 TS-1:WO ₃ :SnO ₂ :V ₂ O ₅ =88 :11:0.7:0.3 Example 9 The denitrification rate and SO ₂ conversion rate were determined for each of the catalysts of Examples 1 to 8 and Comparative Examples 1 to 3 using the following methods. A honeycomb-shaped catalyst (3 cell square, opening 4.6 mm, wall thickness 1.3 mm, length 400 mm) cut into an appropriate size was packed into a stainless steel reaction tube with an inner diameter of 38 mm that was immersed in a molten salt bath. , Synthesis gas having the following composition and NH ₃ added thereto was supplied only to the pores of the catalyst. The NOx concentration before and after the reactor was measured using a chemiluminescent NOx meter (ECL-7S) manufactured by Yanagimoto Seisakusho, and the denitrification rate (%) was calculated according to the following formula. Denitrification rate (%) = Inlet NOx concentration - Outlet NOx concentration / Inlet NOx concentration × 100 Gas amount 0.794Nm ³ /H Space velocity (SV) 5500H ^-1 (Cavity cylinder conversion) NH ₃ /NOx (molar ratio) 1.0 (Table 2) Gas composition NO 200ppm (synthesis gas) O ₂ 4% SO ₂ 800ppm H ₂ O 10% N ₂ remaining Also, the SO ₂ oxidation rate is calculated by reacting the synthesis gas with the composition shown in Table 2 without adding NH ₃ Temperature 350℃,
Measured under the conditions of SV5500H ^-1 . The SO ₃ concentration at the outlet of the reaction tube was determined by the method of Goxoyer et al.
Page, 1961) and was determined by titration with an aqueous barium acetate solution in isopropyl alcohol using Arsenadz as an indicator. In addition, the total SOx of the generated exhaust gas was absorbed in 5% hydrogen peroxide solution and determined in the same manner as the SO ₃ concentration measurement. The SO ₂ oxidation rate (%) was calculated according to the following formula. _SO2 oxidation rate (%) = outlet _SO3 concentration/total SOx concentration x 1
00 The results obtained are shown in Table 3. Examples 10 to 13 The TiO ₂ −SiO ₂ powder used in Example 1, i.e.
A catalyst containing vanadium, tungsten, and tin was prepared according to Example 1 using TS-1 and changing the composition ratio. The denitrification rate and the SO ₂ oxidation rate were determined for each of the catalysts of Examples 10 to 13 and Comparative Examples 4 and 5 according to Example 9. The results obtained are shown in Table 4. Example 14 A honeycomb-shaped catalyst having the same composition as the catalyst of Example 11 (150 mm square, pitch 7.4 mm, wall thickness 1.4 mm, length
A durability test was conducted by connecting six (500 mm) in series and installing them parallel to the gas flow direction, and exposing them to C heavy oil-fired boiler exhaust gas. Test conditions are gas temperature 360℃, space velocity (SV)
5000H ^-1 , gas amount 337.5Nm ³ /H, NH ₃ /NOx = 1.0
(molar ratio), and the exhaust gas composition is NOx130
~150ppm, SOx800~1000ppm, _SO330 ~
50ppm, _O2 2-3%, _H2O10 %, _CO2 10-12%,
There are _N2 left. The denitrification rate and SO ₂ oxidation rate remained unchanged from the initial stage of the reaction even after 6000 hours, and the denitrification rate remained unchanged.
It was found that the oxidation rate was 94-95% and the _SO2 oxidation rate was 0.4-0.5%, indicating excellent durability. Example 15 A honeycomb-shaped catalyst having the same composition as the catalyst of Example 10 (150 mm square, pitch 7.4 mm, wall thickness 1.4 mm, length
500mm) was exposed to coal-fired boiler exhaust gas in the same manner as in Example 14 to conduct a durability test. Test conditions are gas temperature 380℃, space velocity (SV)
5000H ^-1 , gas amount 337.5Nm ³ /H, NH ₃ /NOx = 1.0
(molar ratio), and the exhaust gas composition is NOx250
~340ppm, _SO2 1000~1300ppm, _O2 3~4%,
10% _H2O , 8-10% _CO2 , balance _N2 . Further, dust was contained at 100 mg/Nm ³ (after dust removal using an electrostatic precipitator). The denitrification rate and SO ₂ oxidation rate remained unchanged from the initial stage of the reaction even after 6000 hours, and the denitrification rate was 93-94%, SO ₂
The oxidation rate was 0.3 to 0.4%, indicating excellent durability. Denitration rate and _SO2 oxidation rate

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Claims (1)

[Claims] 1 As a catalyst for selectively reducing nitrogen oxides in exhaust gas by catalytically reacting them with ammonia, a soluble titanium compound is used as a titanium source, a soluble zirconium compound is used as a zirconium source, and a soluble silicon compound and/or silica sol is used as a silicon source. A binary composite oxide consisting of titanium and silicon obtained by forming a coprecipitate through a sum reaction, washing, drying and firing the coprecipitate,
At least one composite oxide selected from the group consisting of binary composite oxides consisting of titanium and zirconium and ternary composite oxides consisting of titanium, silicon and zirconium is used as the catalyst A component, and vanadium oxide is used as the catalyst. B component, tungsten oxide as catalyst C component, and tin oxide and/or tin sulfate as catalyst D component,
The composition is 73-95% by weight for A and 0.3% by weight for B.
~3% by weight, C from 3 to 12% by weight and D from 0.5%
In the range of 10% by weight, tin/tungsten in atomic ratio
In the range of 0.1 to 3.0, furthermore, the composition of component A is 40 to 95% titanium oxide in mole percent as an oxide,
Silicon and/or zirconium oxide 5-60
%.