JPH07213908A - Catalyst for purifying exhaust gas and method therefor - Google Patents

Abstract

PURPOSE:To obtain an exhaust gas purifying catalyst preventing the sudden lowering of leak NH3 decomposing activity caused by volatile compds. of As, Se, Re or the like contained in coal combustion gas and capable of realizing a high denitration rate, low leak NH3 decomposing activity and high CO oxidizing activity and to provide an excellent exhaust gas purifying method using this exhaust gas purifying catalyst. CONSTITUTION:A catalyst compsn. consists of a first component consisting of TiO2 and oxide of one or more kinds of elements selected from Mo, W and V, a second component obtained by preliminarily supporting Pt, Pd and Rh on a porous material such as silica, alumina or zeolite and a third component of sulfate of one or more kinds of elements selected from Al, Mn and Mg, and its characteristic comprises that the mixing wt. ratio of the second and first components is 20/80-0.5/99.5 and the content of the third component is 0-20wt.%. This exhaust gas purifying catalyst having NOx reducing function, unreacted NH3-decomposing function and CO oxidizing function in the presence of NH3 is composed of the above compsn. and adapted to the purification of exhaust gas.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst having a decomposition activity of nitrogen oxides (NOx) in an exhaust gas, an oxidation activity of carbon monoxide (CO) and a decomposition activity of unreacted ammonia, and an exhaust gas purification catalyst using the same. Ammonia that can prevent unreacted ammonia decomposing activity due to vaporization of volatile oxides such as arsenic oxide and can maintain high denitration performance, CO decomposing activity and reduction of unreacted ammonia leakage for a long period of time. TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst using NH ₃ ) as a reducing agent and a method for treating exhaust gas using the same.

[0002]

2. Description of the Related Art NOx in smoke emitted from power plants, various factories, automobiles, etc. is a causative agent of photochemical smog and acid rain, and ammonia (NH ₃ ) is reduced as an effective removal method. The flue gas denitration method by selective catalytic reduction as an agent is widely used mainly in thermal power plants. The catalyst contains titanium oxide (Ti) containing vanadium (V), molybdenum (Mo) or tungsten (W) as an active ingredient.
O ₂ ) -based catalysts are used, in particular, those containing vanadium as one of the active components have not only high activity, but also small deterioration due to impurities contained in exhaust gas,
Since it can be used at lower temperatures, it has become the mainstream of the present denitration catalyst (Japanese Patent Laid-Open No. 50-128681).

From the viewpoint of environmental protection in recent years, the total amount of NOx emission is regulated for fixed generation sources such as large-capacity boilers for power generation, and the NOx amount in exhaust gas discharged from equipment is controlled to an extremely low level for operation. It is becoming essential to do so. For this reason, methods such as increasing the catalyst filling amount and increasing the ammonia injection amount to operate the denitration device at a high denitration rate are being studied in the ammonia reduction type denitration device.
With the demand for such high-level denitration, it has become essential to reduce the amount of unreacted ammonia that has not been used in the denitration reaction (hereinafter, leakage ammonia) to the same level as the NOx level. The high denitrification rate operation inevitably increases the amount of leaked ammonia. For this reason,
In order to reduce the amount of leaked ammonia, installation of a decomposition catalyst and uniform injection / mixing of ammonia are being studied. The inventors of the present invention also invented a denitration catalyst having ammonia decomposing activity, which comprises a porous body supporting a noble metal and a titanium oxide-based composition, and uses it to realize a high denitration rate, high CO oxidation activity, and low leak ammonia concentration. We have applied for a method for purifying the exhaust gas that can be produced (Japanese Patent Application No. 3-312308, Japanese Patent Application No. 4-138514, etc.).

[0004]

The catalyst developed by the present inventors, which is the above-mentioned conventional technique, has a very high denitration rate and a high C ratio when purifying a relatively clean exhaust gas such as a gas fired boiler.
It had excellent properties that could achieve O-oxidation activity and low leak ammonia concentration, but sufficient measures were taken when volatile oxides such as arsenic, selenium, and rhenium were contained in the exhaust gas such as coal exhaust gas. Not taken into consideration, there was a problem that the decomposition rate of leaked ammonia decreases with time. In FIG. 4, a denitration catalyst having the activity of decomposing leaked ammonia, which is disclosed in Japanese Patent Application No. 4-138514, is applied to coal gas at about 80%.
The time-dependent changes in the denitration rate and the decomposition activity of leaked ammonia after exposure for 00 hours are shown together with the change in the amount of arsenic accumulated in the catalyst. Although the decrease in denitration rate over time is slight,
A phenomenon is observed in which the decomposition activity of leaked ammonia rapidly decreases as arsenic compounds accumulate on the catalyst. The object of the present invention is to solve the problem of conventional catalysts, namely, to rapidly reduce the leak ammonia decomposing activity due to volatile compounds such as arsenic (As), selenium (Se) and rhenium (Re) contained in coal combustion gas. It is an object of the present invention to provide an exhaust gas purifying catalyst which can prevent and realize a high denitration rate, a leak ammonia decomposing activity and a high CO oxidizing activity, and an excellent exhaust gas purifying method using the same.

[0005]

The above objects of the present invention can be achieved by the following constitutions. That is, a composition comprising a titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten and vanadium is a first component, and a noble metal such as platinum, palladium or rhodium is previously loaded on a porous body such as silica, alumina or zeolite. A catalyst composition containing the second component, and one or more sulfates selected from aluminum, manganese, and magnesium as the third component, wherein the mixing weight ratio of the second component and the first component is 20/8.
In the range of 0 to 0.5 / 99.5, the content of the third component is more than 0 and 20 wt% or less, the reduction function of nitrogen oxides in the presence of ammonia and the decomposition function of unreacted ammonia Exhaust gas purifying catalyst having a function of oxidizing carbon oxide, or nitrogen oxidation in exhaust gas containing at least one volatile oxide of arsenic, selenium or rhenium, using the exhaust gas purifying catalyst as at least a part of the exhaust gas denitration catalyst layer A method for purifying exhaust gas, in which an ammonia reduction treatment of a substance, a decomposition treatment of unreacted ammonia and an oxidation treatment of carbon monoxide are performed,
Alternatively, by installing the exhaust gas purification catalyst layer in the downstream of the denitration catalyst layer for catalytic reduction removal of nitrogen oxides in the exhaust gas containing carbon monoxide and nitrogen oxides in the presence of ammonia, This is a method for purifying exhaust gas by decomposing and removing unreacted ammonia and carbon monoxide. Since the oxidative decomposition performance of unreacted ammonia is high in the exhaust gas purification method of the present invention, it is desirable to exhibit high denitration performance when operated at a molar ratio of ammonia and nitrogen oxides of 0.8 or more.

The following components are used as the components of the catalyst of the present invention. In addition, the concentration of the noble metal element exceeds 0 and exceeds 10
The three components were kneaded in the presence of water so that the content of the third component sulfate was more than 0 and 20 wt% or less in the range of 00 ppm or less, and then formed into a plate-like or honeycomb-like sulfate. What is calcined below the decomposition temperature of is used as a catalyst. (A) First component Ti-V, Ti-Mo, Ti-W, Ti-V-W, Ti
-Oxide of Mo-V combination. (B) Second component A composition in which one or more noble metal elements selected from platinum, palladium, and rhodium are previously supported on zeolite, porous silica, porous alumina, etc. by ion exchange impregnation. (C) Third component Aluminum sulfate, manganese sulfate, magnesium sulfate or a hydrate thereof.

It goes without saying that any method can be used as the method for preparing the purification catalyst (denitration catalyst) of the present invention having the above-mentioned structure, as long as the structure can be realized. However, a better catalyst can be obtained by using the following method. Among the catalyst components, the first component may be various ones as described above, but particularly Ti-V and Ti-VM as the catalyst component.
Good results are obtained when an oxide catalyst composed of an element such as o or Ti-W-V is used. These are prepared by adding salts such as oxyacid salts of V, Mo, and W to a slurry of hydrous titanium oxide such as metatitanic acid, making a paste while evaporating water using a heating kneader, and drying at 400 ° C. From 70
It is obtained by firing at 0 ° C. and crushing if necessary.

The second component is prepared by carrying it in advance in porous micropores such as zeolite, silica and alumina by ion exchange or kneading. Porous mordenite, clinoptilolite, erionite, Y-type zeolite and other hydrogen-substituted compounds, sodium-substituted compounds, calcium-substituted compounds and other zeolites used as the second component, having a surface area of 10
0 m ² / g to 500 m ² / g silica, alumina, etc. can be used. The particle size at the time of use is preferably about 1 to 10 μm, and it can be crushed and used in advance. The noble metal is immersed in an aqueous solution in which the noble metal is dissolved in the form of chloride, nitrate or ammine complex and ion-exchanged or evaporated to dryness together with the aqueous solution to form 0.01 wt% to 0.1 wt% of the noble metal.
It is supported by wt% and used as it is, or by firing it to decompose the noble metal salt into noble metal. The third component is selected from aluminum sulfate, manganese sulfate and magnesium sulfate 1
One or more types of sulfates or hydrates thereof, which are used as powder or, if necessary, dissolved in water in advance.

The first and second components are in a weight ratio of second component / first component of 20/80 to 0.5 / 99.5, preferably 1
The range of 0/90 to 1/99 is suitable, and the third component is added to this in an amount of more than 0 and up to 20 wt%, and well known as water and an inorganic binder, a molding aid, an inorganic fiber, etc. The moldability improver is added and kneaded with a kneader such as a kneader to form a paste. The obtained paste-like catalyst is applied to a mesh-like substrate made of an inorganic fiber, a metal substrate roughened by thermal spraying or the like to form a plate-like catalyst, or formed into a columnar shape or a honeycomb shape by an extrusion molding machine. The molded body is dried at a temperature at which sulfate remains as sulfate, usually 450 ° C to 5 ° C.
It is used after firing at 50 ° C. In addition to the above method, the same effect can be obtained by obtaining a catalyst body composed of the first component and the second component in advance with the above composition and then impregnating this with an aqueous solution of the third component. Further, the obtained exhaust gas purification (denitration) catalyst also has CO oxidation activity in the exhaust gas.

As shown in FIG. 1, the obtained catalyst body is packed in the catalyst layer of the reactor 2 or in the whole layer or in a part thereof in combination with the conventionally known denitration catalyst, and the NOx concentration in the exhaust gas is increased. NOx as a denitration catalyst in the high
In a region where the concentration is low, it acts as a decomposition catalyst for unreacted (excess) ammonia. The use conditions are not particularly limited, but the effect of reducing the leak ammonia, which is a feature of the catalyst of the present invention, is large because the molar ratio of NOx in the exhaust gas to NH ₃ which is the reducing agent (NH ₃ / NOx ratio) is large. This is a case of 0.8 or more, which is suitable for a denitration device that operates at a high denitration rate. The second component / first component ratio is particularly important in the present invention, and is selected from the above-mentioned range by using zeolite, silica, alumina or the like having a large amount of precious metal supported so that the second component / first component ratio becomes small. And the amount of precious metal supported on the entire catalyst is 1 to 1.
000 ppm, preferably in the range of 10 to 100 ppm gives good results. This is because the micropores formed by the second component are sparsely present in the macropores formed by the first component, and NH ₃ is selectively adsorbed on the first component to facilitate the use in the denitration reaction. Further, reducing the amount of noble metal also has the effect of facilitating separation depending on the presence or absence of the catalyst unit price.

The larger the amount of the third component added, the greater the effect of preventing the reduction of the NH ₃ decomposition activity by volatile oxides such as arsenic oxide, but if the amount of the third component added is too large, the denitration rate will decrease. Therefore, as a sulfate, it exceeds 20 and is 20 wt%.
Good results are obtained when added in an amount of up to, preferably from 2 to 15 wt%. Also, the second component / first component ratio is selected small when the entire catalyst layer of the reactor 2 of FIG. 1 is composed of the catalyst of the present invention, and the catalyst layer of the reactor 2 is combined with a conventional denitration catalyst. Therefore, when the catalyst of the present invention is used in a part of the catalyst layer, it is easy to obtain a good result by selecting a large second component / first component ratio and at the same time increasing the precious metal content.

[0012]

The exhaust gas purifying catalyst of the present invention is shown in FIGS.
As shown in Fig. 2, a denitration catalyst layer is formed on the entire catalyst layer in the reactor 2 or in combination with a known denitration catalyst such as a conventional titanium oxide-based catalyst to form NOx containing NH ₃ as a reducing agent. Reduction reduction and CO oxidation removal are performed.
Unreacted NH ₃ is oxidatively decomposed into nitrogen and water to reduce leak ammonia. On the inner surface of the pores of the catalyst according to the present invention used for a part or all of the catalyst layer in the reactor 2 shown in FIG. 1, porous materials such as silica in which a precious metal is supported in the denitration catalyst component are scattered. When the NOx concentration is high due to the action of the peculiar inner surface of the pores, the structure acts as a normal denitration catalyst, the NOx concentration decreases, and the Nx concentration decreases.
When H ₃ becomes excessive, it acts as a decomposition catalyst of NH ₃ and a CO oxidation catalyst. That is, when the NOx concentration is high and the denitration reaction rate is high, the NH ₃ adsorbed on the denitration catalyst component of the present invention is quickly consumed, so that the NH ₃ in the gas phase is
Are successively adsorbed preferentially on the purification catalyst component. On the other hand, in the catalyst in the region where the NOx concentration has decreased due to the progress of the NOx removal reaction, NH adsorbed on the NOx removal catalyst component surface by NOx
_Since the consumption rate of ₃ is small, ammonia in the gas phase is hardly adsorbed by the denitration catalyst component and is preferentially oxidized on the surface of the noble metal to be converted to NOx. NH NOx produced by the oxidation of NH ₃ is adsorbed on the denitration catalyst component surfaces ₃
Is reduced and decomposed into nitrogen and water. As described above, when the amount of unreacted ammonia is larger than that of NOx, the catalyst of the present invention has a characteristic that it acts as a decomposition catalyst of unreacted ammonia by the action of the porous body supporting the noble metal and the concerted action of the denitration catalyst component. is there. Further, since CO contained in the exhaust gas has a property of easily diffusing in the catalyst pores, it is quickly contacted with an oxidizing component in the catalyst to be oxidized into CO ₂ .

Even in the conventional catalyst developed by the present inventors, which does not contain the third component, which is a characteristic of the catalyst of the present invention, NH
The decomposition action of ₃ proceeds similarly. However, when the conventional catalyst is used in the exhaust gas containing a trace amount of volatile oxides such as arsenic and selenium such as coal combustion exhaust gas, the vapor of the volatile oxide is adsorbed by the noble metal and is indispensable for the decomposition process of unreacted ammonia. The above-mentioned NH ₃ oxidation reaction (NOx generation reaction) is hindered, causing a sharp decrease in the decomposition rate of NH ₃ , which is not practical. The present inventors have elucidated the above mechanism that the conventional catalyst developed by the present inventors is deteriorated by a volatile oxide (mainly arsenic oxide), and at the same time, NH ₃
We searched for a component effective in preventing the degradation of the decomposition activity and found the above-mentioned third component. Sulfates such as aluminum sulphate, manganese sulphate, magnesium sulphate, etc., which are the third component, significantly prevent the inhibition of NH ₃ oxidation due to the adsorption of arsenic oxide vapor on the noble metal (oxidation catalyst component), which results in a high long-term It is possible to realize a catalyst that can maintain the leak ammonia decomposing activity. Further, the sulfate as the third component has the function of increasing the binding of the catalyst particles and reducing the wear due to the large amount of combustion ash contained in the coal combustion gas, which also contributes to the extension of the life of the catalyst.

[0014]

Embodiments of the present invention will be described with reference to the drawings. (Overall Configuration of Exhaust Gas Purification System) An exhaust gas purification system of the present invention is shown in FIG. Exhaust gas from the boiler 1 is denitrated in the reactor 2, heat-exchanged in the heat exchanger 3, and then collected in the dust collector 4 and discharged from the chimney 5 into the atmosphere. At this time, ammonia is supplied from the injection line 6 to the exhaust gas passage on the upstream side of the reactor 2. When only the exhaust gas purifying catalyst 7 according to the present invention is filled in the catalyst layer in the reactor 2 (FIG. 1 (a)), the exhaust gas purifying according to the present invention is provided on the downstream side of the conventionally known normal denitration catalyst 8. When the catalyst 7 is filled (FIG. 1B), and when the exhaust gas purifying catalyst 7 of the present invention is filled between the well-known normal denitration catalyst 8 (FIG. 1).
There is (c)). Since the exhaust gas purifying catalyst 7 according to the present invention has a leak ammonia decomposing activity, the unreacted ammonia in the exhaust gas can be removed even if the exhaust gas purifying catalyst 7 is arranged on the downstream side of the conventionally known denitration catalyst 8 having no leak ammonia decomposing activity. Can be decomposed and purified. Hereinafter, a method for producing the exhaust gas purifying catalyst 7 and an example of using the same for exhaust gas purification will be described in detail.

Example 1 Slurry of metatitanate (TiO ₂ content: 30 wt%, S
O ₄ content: 8 wt%) 67 kg of ammonium paratungstate _{((NH 4) 10 H 10} · W 12 O 46 · 6H 2 O)
3.52 kg and Ammon metavanadate 0.6
3 kg was added, and the mixture was kneaded while evaporating water using a heating kneader to obtain a paste having a water content of about 36%. This is 3mm
After extruding into a columnar shape of φ and granulating, dry with a fluidized bed dryer,
Then, it was baked in the air at 550 ° C. for 2 hours. The obtained granules were pulverized with a hammer mill to a particle size of 1 μm to 60% or more to obtain a denitration catalyst powder as the first component. The composition at this time is V /
W / Ti = 2/5/91 (atomic ratio). On the other hand, chloroplatinic acid (H ₂ [PtCl ₆ ] .6H ₂ O) 0.665 g was dissolved in 1 liter of water, and high surface area fine silica (manufactured by Tomita Pharmaceutical Co., Ltd .: Microcomputer F (trade name)) 500 g
Was added and evaporated to dryness on a sand bath to support Pt. This one
After drying at 80 ° C. for 2 hours, it was baked at 500 ° C. for 2 hours,
05 wt% Pt-silica was prepared and used as the second component.

Separately from this, a mesh of plain weave of 1400 E glass fibers having a fiber diameter of 9 μm with a mesh opening of 10 / inch is filled with a slurry of 40% titania, 20% silica sol and 1% polyvinyl alcohol. The catalyst base material was obtained by impregnation and drying at 150 ° C. to impart rigidity. First component 20k
g, the second component 408 g, and aluminum sulfate hydrate (A ₁₂ (SO ₄ ) ₃ content 53 wt%) as the third component 3.
35 kg was taken, 5.3 kg of silica / alumina inorganic fibers and 17 kg of water were added and kneaded with a kneader to obtain a catalyst paste. The paste-like catalyst mixture prepared between the two base materials was placed and passed by a pressure roller to press-bond the catalyst between the stitches and the surface of the base material to obtain a plate-like catalyst having a thickness of 1 mm. The obtained catalyst was dried at 180 ° C. for 2 hours and then calcined in the air at 460 ° C. for 2 hours. The second component / first component ratio of the first component and the second component in this catalyst was 2/98, and the Pt content was 10 pp excluding the catalyst base material and the inorganic fiber.
Corresponds to m. The amount of the third component added corresponds to about 8%.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that the third component was not added. Examples 2 to 6 Addition amount of aluminum sulfate, which is the third component of the examples, 8w
A catalyst was prepared in the same manner as in Example 1 except that t% was changed to 2, 4, 12, 16, 20 wt%. Test Example 1 The catalysts of Examples 1 to 6 and Comparative Example 1 were cut into a piece having a width of 20 mm and a length of 100 mm.
After filling one sheet and changing NH ₃ under the conditions shown in Table 1, the denitrification rate and the concentration of leaked ammonia detected at the outlet of the reactor 2 were measured. Following this, in order to accelerate the catalyst deterioration due to volatile oxides such as arsenic oxide contained in the coal exhaust gas and perform the test, an arsenic oxide (As ₂ O ₃ ) aqueous solution was added to the gas of the composition shown in Table 1. It was prepared by evaporation so that the As ₂ O ₃ concentration was 50 ppm. This condition was maintained for 5 hours, and arsenic oxide was adsorbed on the catalyst to examine the change in the catalyst performance.

[0018]

[Table 1] The obtained results are summarized in the relationship between the amount of aluminum sulfate added, the denitration rate and the decomposition rate of unreacted ammonia, and are shown in FIG.

The decomposition rate of unreacted ammonia depends on the reactor 2
It was calculated by the following formula from NOx and ammonia detected at the outlet. Unreacted NH ₃ decomposition rate _{(%) = ([NH 3} ] in- [NH 3] d
_{enox- [NH 3] out) /} ([NH 3] in- [NH 3] deno
x) × 100 [NH ₃ ] in: NH ₃ concentration at the inlet of the reactor [NH ₃ ] out: NH ₃ concentration at the outlet of the reactor (leak ammonia concentration) [NH ₃ ] denox: NH ₃ concentration used in the denitration reaction It can be seen from No. 2 that the catalyst of Comparative Example 1 undergoes an accelerated test with an As ₂ O ₃ -containing gas, but the denitration activity hardly changes, but the decomposition activity of unreacted ammonia is greatly reduced. On the other hand, in the catalysts of Examples 1 to 6 according to the present invention, the decrease in the unreacted ammonia decomposition rate was remarkably reduced as the amount of aluminum sulfate added was increased, and the durability was improved. Also, from the figure, if the addition amount of aluminum sulfate is small, the deterioration preventing effect is small, and if it is too large, the denitration rate tends to decrease, and particularly good results are obtained when the addition amount is selected in the range of 2 to 15 wt%. Understand.

Examples 7 and 8 The silica powder in Example 1 was replaced with an H-type mordenite powder having a SiO ₂ / Al ₂ O ₃ ratio (mol / mol) of 15 and a γ-alumina powder, and the others were the same as in Example 1. Similarly, the second component was prepared. Comparative Examples 2 and 3 Catalysts were prepared in the same manner as in Examples 7 and 8 except that the third component in Examples 7 and 8 was not added. Examples 9 and 10 Instead of the aluminum sulfate of Example 1, manganese sulfate (M
A catalyst was prepared in the same manner as in Example 1 except that nSO ₄ .5H ₂ O) 2.83 kg and magnesium sulfate (MgSO ₄ ) 1.77 kg were used.

Example 11 In place of ammonium paratungstate in the first component preparation method of Example 1, ammonium paramolybdate ((N
A catalyst was prepared in the same manner as in Example 1 except that H ₄ ) ₆ · Mo ₇ O ₂₄ · 4H ₂ O) was used. Comparative Example 4 A catalyst was prepared in the same manner as in Example 11 except that the third component, aluminum sulfate, was not added. Examples 12 and 13 Chloroplatinic acid in Example 1 was treated with palladium nitrate (Pb).
(NO ₃ ) ₃ ) and rhodium nitrate (Rh (NO ₃ ) ₃ )
The above nitric acid solution was used to prepare silica having a supported amount of palladium or rhodium of 0.05 wt%. This is Example 1
The catalyst was prepared in the same manner as in Example 1 except that Pt-silica was used. Comparative Examples 5 and 6 A catalyst was prepared in the same manner as in Examples 12 and 13 except that the third component in Examples 12 and 13 was not added. Test Example 2 The same tests as in Test Example 1 were conducted on the catalysts of Examples 1 and 7 to 13 and the catalysts of Comparative Examples 1 to 6, and the results are shown in Table 2 together with the catalyst composition.

[0022]

[Table 2] As is clear from Table 2, the catalyst according to the present invention does not depend on the type of the first component, the type of the noble metal as the second component, and the carrier thereof, and compared with the catalyst of the comparative example, an accelerated test using As ₂ O ₃ vapor. Even after that, the leaked ammonia concentration is low, and it has excellent durability to maintain a high unreacted ammonia decomposing activity.
Further, it is found that not only aluminum sulfate but also manganese sulfate and magnesium sulfate have similar effects.

Test Example 3 When the accelerated deterioration test shown in Test Example 1 was performed on the catalyst of Example 1 and the catalyst of Comparative Example 1, and the deteriorated catalyst was changed in the NH ₃ injection amount under the conditions shown in Table 1. And the outflow concentration of unreacted ammonia at the outlet of the reactor 2 were measured. The obtained results are shown in FIG. 3 in comparison with each other. In the comparative catalyst, when the NH ₃ injection amount was increased and the NH ₃ / NO ratio was increased, the denitration rate was increased and the outflow concentration of unreacted ammonia was significantly increased. On the other hand, with the catalyst according to the present invention, NH ₃
It can be seen that there is almost no outflow of unreacted ammonia even if the / NO ratio is increased, and a high denitration rate and low leak ammonia can be realized. Furthermore, the effect of the present invention is remarkable when operating at a denitrification rate where the NH ₃ / NO ratio is 0.8 or more.

Test Example 4 The catalysts of Example 1 and Comparative Example 1 were subjected to the accelerated deterioration test of Example 1, and the effect of improving durability against the decrease in CO oxidation rate before and after the test was observed. CO in reaction gas is 200pp
CO _{2 under} the conditions shown in Table 1
The oxidization rate of the above was measured, and the results are summarized in Table 3.

[Table 3] As is clear from this figure, the method of the present invention is excellent not only for preventing the reduction of ammonia decomposing activity but also for preventing the reduction of CO oxidizing activity. As described above, the purification catalyst 7 of the present invention has high denitration activity, high CO oxidation activity, and leak ammonia decomposition activity even for exhaust gas containing volatile oxide vapor as a catalyst poison, and is useful as an exhaust gas purification catalyst.

[0025]

INDUSTRIAL APPLICABILITY As described above, the catalyst according to the present invention is used for treating coal combustion exhaust gas containing volatile oxide vapor such as arsenic oxide as a catalyst poison, industrial waste combustion furnace exhaust gas, and waste incinerator exhaust gas treatment. Even if it is used, the decomposition activity of unreacted ammonia does not decrease for a long period of time, and it can be used for reducing ammonia leaking from the denitration reactor. As a result, high denitration rate
It is possible to realize a denitration device that can be operated under conditions of low leak ammonia.

[Brief description of drawings]

FIG. 1 is a system diagram of a denitration device using a catalyst according to the present invention.

FIG. 2 is a diagram comparing durability of an example and a comparative example catalyst.

FIG. 3 is a diagram showing an effect when the example is used in a denitration device.

FIG. 4 is a supplementary diagram showing a problem of a conventional catalyst.

[Explanation of symbols]

1 ... Boiler, 2 ... Reactor, 3 ... Heat exchanger, 4 ... Dust collector,
5 ... Chimney, 6 ... Ammonia injection line, 7 ... Purification catalyst of the present invention, 8 ... Conventionally known denitration catalyst

Claims (6)

[Claims] 1. A composition comprising a titanium oxide and an oxide of one or more elements selected from molybdenum, tungsten and vanadium is used as a first component, which is preliminarily added to a porous material such as silica, alumina or zeolite by platinum, palladium or rhodium. What is claimed is: 1. A catalyst composition comprising a noble metal supported as a second component, and one or more sulfates selected from aluminum, manganese and magnesium as a third component, wherein the mixing weight ratio of the second component and the first component is 20 /. 80-0.5 / 99.5
And the content of the third component exceeds 0 and is 20 wt.
% Or less, an exhaust gas purifying catalyst having a reducing function of nitrogen oxides in the presence of ammonia, a decomposing function of unreacted ammonia, and an oxidizing function of carbon monoxide. 2. The precious metal content of the exhaust gas purifying catalyst is 10
2. The range is less than 00 ppm.
Exhaust gas purification catalyst described. 3. The exhaust gas purifying catalyst according to claim 1 or 2 is used for at least a part of an exhaust gas denitration catalyst layer, and nitrogen oxides in exhaust gas containing at least one volatile oxide of arsenic, selenium or rhenium are contained. A method for purifying exhaust gas, which comprises performing an ammonia reduction function, an unreacted ammonia decomposition treatment, and a carbon monoxide oxidation treatment. 4. The molar ratio of ammonia to nitrogen oxide is 0.
The method for purifying exhaust gas according to claim 3, wherein the method is operated at 8 or more. 5. The method according to claim 1, wherein the nitrogen oxide in the exhaust gas containing carbon monoxide and nitrogen oxides is catalytically reduced in the presence of ammonia in a downstream portion of a denitration catalyst layer. A method for purifying exhaust gas, which comprises installing the exhaust gas purifying catalyst layer as described above, and decomposing and removing unreacted ammonia and carbon monoxide as well as a function of reducing nitrogen oxides in the exhaust gas. 6. A molar ratio of ammonia to nitrogen oxides of 0.
The method for purifying exhaust gas according to claim 5, wherein the method is operated at 8 or more.