JPS585703B2 - Chitsusosankabutsujiyokiyoshiyokubai - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for removing nitrogen oxides (hereinafter abbreviated as NOx) contained in gas.

In particular, the present invention adds ammonia to a harmful gas containing NOx and sulfur compounds (mainly sulfur dioxide, hereinafter abbreviated as SOx) at the same time, and causes a catalytic reaction.
The present invention provides a catalyst that efficiently reduces NOx to harmless nitrogen without being poisoned by SOx, and has excellent durability.

Thermal power plants and other industrial facilities use heavy oil and coal containing sulfur and nitrogen compounds as fuel sources for boilers and other equipment, and use air as an oxygen source, so N is present in the exhaust gas.
It contains Ox and SOx, which cause environmental pollution.

Therefore, research and development on techniques for removing SOx and NOx from the exhaust gas are being advanced in various fields, and many specific methods have been proposed.

These methods can be roughly divided into wet methods and dry methods, but among the above harmful substances, desulfurization technology as a method for removing SOx is
Since the regulation of Ox has preceded the regulation of exhaust NOx, technological progress has been rapid, and it has been established mainly as a wet desulfurization method.

However, the denitrification method as a NOx removal method has not yet been completed as a technology, and various methods are being proposed one after another.

The development research regarding these proposed NOx removal technologies is as follows:
They are adsorption method, absorption method and catalytic reduction method.

First, the adsorption method is a method of adsorbing and removing NOx using synthetic zeolite, activated carbon, or ion exchange resin as an adsorbent, but because the adsorption capacity is limited, it is affected by coexisting gases such as sulfur compounds and water vapor. There are problems such as the need to frequently regenerate the adsorbent and the fact that the exhaust gas treatment capacity is generally small, resulting in a large-scale device.

Next, the absorption method is the oxidation absorption method, which oxidizes and absorbs NOx, and the N
There is a reduction absorption method that reduces and absorbs Ox, but the oxidation absorption method uses an alkaline aqueous solution containing an oxidizing agent such as sodium hypochlorite, hydrogen peroxide, sodium dichromate, or potassium permanganate. Another method is to oxidize with ozone or catalytic oxidation, and then absorb with an alkaline aqueous solution.

Further, the reduction absorption method is a method in which NOx is reduced and removed to N2 by contacting with an aqueous solution containing a reducing agent such as sodium sulfite, sodium thiosulfate, or sodium sulfide.

These absorption methods have poor absorption efficiency when dealing with large amounts of exhaust gas because the concentration of NOx is dilute, resulting in large-scale equipment.Furthermore, consideration must be given to wastewater treatment of the aqueous solution used for absorption. There are many problems in practical application of the process.

In contrast to these methods, the catalytic reduction method is a method in which exhaust gas is treated with various reducing agents to reduce NOx to harmless nitrogen, and is promising because it solves the shortcomings of the above methods.

By the way, there are various catalytic reduction methods depending on the reducing agent used, but they can be broadly divided into non-selective catalytic reduction, which also reduces oxygen coexisting in the exhaust gas, and selective catalytic reduction, which selectively reduces only NOx. Ru.

In the former case, hydrocarbons such as methane, LPG, hydrogen, or carbon monoxide are used as reducing agents.
Generally, 2 to 6% oxygen coexists in exhaust gas from boilers, etc., and reducing dilute NOx requires a large amount of reducing agent, which is not economical.Furthermore, the reaction heat associated with the reduction reaction is There are many problems, such as making it difficult to control the reaction temperature.

On the other hand, in the latter case, using ammonia as a reducing agent selectively reduces only NOx, which is economical as only a small amount of reducing agent is needed, and the heat of reaction is extremely low, and furthermore, NOx is generated by the reaction. The materials used are harmless nitrogen and water, which is extremely advantageous compared to the above-mentioned methods.

This selective catalytic reduction method using ammonia as the reducing agent is a generally well-known method, but the problem with this method is whether the catalyst can be changed to suit the composition and properties of the exhaust gas to be treated. .

The first physical property that the catalyst should have in this method is that the exhaust gas contains oxygen, sulfur compounds, carbon dioxide, water vapor, etc., but it selectively only produces NOx without being affected by these coexisting gases. The second reason is that the treatment temperature is approximately 400°C considering thermal efficiency since the temperature at the outlet of the economizer attached to the boiler system is generally approximately 400°C. Thirdly, it must be able to perform the reduction at the lowest possible temperature below °C, and thirdly, it must work satisfactorily at a high space velocity (this space velocity is related to the volume of the catalytic reactor, and the larger it is, the more compact the device can be). On the other hand, the pressure drop also increases, so a high standard is required in terms of performance as well as problems with the shape of the catalyst.

), Fourth, soot and dust exist in exhaust gas, and although this soot is mostly carbon, it also contains various heavy metals including iron, so even if the soot and dust adheres to the catalyst, the catalyst will not be covered. It is necessary not to be poisoned.

Although there are other characteristics that a catalyst should have in addition to these four points, the above four points are the important characteristics.

Currently, the desulfurization method has been established as a wet process as an exhaust gas purification system, and when considering the removal of NOx from boiler exhaust gas after desulfurization, it is necessary to introduce the exhaust gas, which has been cooled in the wet process, to a dry catalytic reduction process. must be heated, and considering the amount of heat involved, it is most desirable to be able to perform direct dry catalytic reduction before desulfurization, and for this purpose, it is necessary to avoid being poisoned by sulfur oxides such as S02 mentioned in item 1 of the above 4 points. Developing catalysts will be of paramount importance.

In the selective catalytic reduction method using ammonia as the reducing agent,
Conventionally well-known catalysts include catalysts in which precious metals such as platinum and palladium are supported on activated alumina, but these catalysts do not contain sulfur compounds, especially sulfur compounds, such as oxygen, carbon dioxide, and water vapor, which coexist in the exhaust gas. by N
There is a drawback that the catalytic activity decreases over time due to the influence of the reduction activity of Ox.

On the other hand, the present inventors have investigated that a catalyst in which copper oxide, etc., which is known as a heavy metal catalyst, is supported on a high surface area carrier such as activated alumina, has been found to be effective at reducing sulfur compounds present in exhaust gas, especially sulfur oxides. It was observed that the catalytic activity decreased over time due to poisoning.

This type of catalyst is also known as a sorbent for removing sulfur oxides from exhaust gas, for example as disclosed in British Patent No. 1,089,716, and according to the inventors' study, the catalyst As sulfur content accumulates over time, copper oxide changes to copper sulfate, and a part of activated alumina changes to aluminum sulfate, and these changes eventually affect catalyst activity and cause a decline over time. It turned out to be something.

In other words, activated alumina cannot be used as a carrier as it is, and if it is used, it must be used in a form that will not accumulate sulfur content, or the catalyst will not be affected at all even if it accumulates. It was confirmed that this was the case.

In view of the above, the present inventors added ammonia to the exhaust gas to achieve high efficiency at relatively low temperatures and high space velocities without being particularly affected by sulfur compounds such as coexisting sulfur compounds, oxygen, carbon dioxide vapor, and dust. As a result of our research into a durable catalyst that can effectively reduce and remove NOx to harmless nitrogen, we have developed a catalyst that is completely unaffected by SO2 or SO3, instead of the high surface area active alumina support that was conventionally used as a known support. A low surface area inert carrier having a surface area of 10 m2/g or less by the BET method is used, and a catalyst material consisting of titanium, vanadium, or phosphorus added thereto is simultaneously supported on this carrier, and the titanium is prepared in advance, The present invention was completed by discovering that a catalyst characterized by being made of titanium oxide (TiO2) having a surface area of at least 10 m2/g by the BET method overcomes the above-mentioned drawbacks and maintains excellent purification ability over a long period of time.

The catalyst carrier used in the present invention is already widely used as a catalyst carrier for the catalytic gas phase oxidation reaction for synthesizing phthalic anhydride, maleic anhydride, and ethylene oxide from orun-xylene, naphthalene, benzene, and ethylene, respectively. The main materials are α-alumina, silicon carbide, silicon nitride, zirconia, titanium oxide, magnesium silicate, aluminum silicate, mullite, cordierite, etc., and these are sintered alone or molded and sintered using these basic materials with a small amount of binder. An inert support with a low surface area of less than 10 m2/g, preferably less than 3 m2/7, particularly preferably less than 1 m2/g, is used.

The shape of the carrier may be spherical, cylindrical, cylindrical, irregular, etc., and depending on the design specifications of the reaction vessel, an integrated carrier such as a plate, ribbon, lattice, wave, etc. can be used.

Particularly preferred and easily available carriers include SA5205, 5215, and 5218 sold by Norton.
Examples include low surface area α-alumina carriers, such as .alpha.-alumina carriers, and carriers with high surface roughness and porosity, such as self-sintered silicon carbide.

In the catalyst of the present invention, the amount of the catalyst substance supported is 3 to 50% by weight, preferably 5 to 40% by weight, based on the carrier, and the titanium component of the catalyst substance is 50 to 50% by weight in terms of titanium oxide. 99% by weight, the vanadium component is 1 to 30% by weight converted to vanadium pentoxide (V2O5),
If necessary, the phosphorus component can be changed to phosphorus pentoxide (P2O5).
It contains up to 30% by weight of the total catalyst material.

The titanium compound used in the present invention is a TiO2 powder having a uniform and small particle size and a large surface area in order to be firmly supported on a carrier.

Although fine TiO2 is commercially available, it is generally obtained by the following method.

(1) A method in which titanite such as ilmenite or titanium slag is digested with sulfuric acid and metatitanic acid obtained after hydrolysis is calcined.

(2) A method of oxidatively decomposing titanium tetrachloride.

(3) Titanium ammonium sulfate ((NH
4) Pyrolysis method of 2.SO4.TiO.SO4.H2O]5.

(4) A method in which an organic titanium compound such as titanium tetrachloride, titanium nitrate or tetraisopropyl titanate is hydrolyzed and then fired.

(5) A method in which commercially available reagent-grade titanium sulfate or titanium oxide sulfate is thermally decomposed or hydrolyzed and then calcined.

Of the TiO2 obtained in this way, the present invention is particularly suitable for TiO2 having a surface area of at least 10 m2/g, preferably 2
Good results can be obtained by using a material with a density of 0 m2/g or more.

It is also possible to prepare and use a high surface area TiO2 mixture by suitably mixing high surface area TiO2 of 50 m2/g or more and Ti02 of about 10 m2/g.

Regarding TiO2, the crystal form does not matter; it is generally preferable to use the anatase type, which has a high surface area, as well as the rutile type, and in the case of a mixed type of both types, one with a high anatase content is preferable.

As the titanium compound, in addition to the above-mentioned TiO2, it is also possible to use a titanium compound that decomposes under heating to form TiO2.

Namely, titanium tetrachloride, titanium sulfate, titanyl sulfate,
Titanium oxalate, organic titanate, and the like can also be used alone or in an aqueous solution or an acidic aqueous solution.

Suitable starting materials for vanadium and phosphorus components include oxides, hydroxides, inorganic acid salts, organic acid salts, oxyacids, and oxyacid salts, especially ammonium salts, oxalates, and nitrates. , sulfates, halides,
and oxides are used in the form of an aqueous solution or a slurry dispersed in water or a solvent.

Further, as the phosphorus component, phosphoric acid, inorganic phosphates, organic phosphates, organic phosphorus compounds, etc. are used.

Further, as the phosphorus compound, titanium phosphate, which is a compound of phosphorus and titanium, or vanadium and phosphorus composite oxide can also be used.

The catalyst of the present invention makes it possible to prevent catalyst activity deterioration due to SOx present in NOx-containing gas by supporting a catalyst component such as titanium, vanadium, or phosphorus on an inert carrier. However, to mention other characteristics of the catalyst of the present invention, the first is that NH3 of NOx
The second reason is that the oxidizing activity from SO2 to SO3 is significantly suppressed even in the coexistence of oxygen gas.

The first feature relates to important performance that is essential for NOx reduction catalysts, but the second feature is also very important industrially and has traditionally been a major problem in NOx purification measures in the coexistence of SO2. Ta.

In other words, suppressing the oxidation of SO2 to SO3 means that it is possible to prevent the dew point temperature from rising due to the SO3 present in the reduced gas, making it possible to perform heat exchange using a heat exchanger more economically. This is because it is extremely advantageous industrially in terms of preventing material deterioration due to SO3, and the catalyst of the present invention has also been greatly improved in this respect.

In order to take advantage of the above-mentioned characteristics of the catalyst of the present invention, the catalyst is prepared as follows.

Using vanadium, titanium, or the above-mentioned catalyst raw material with phosphorus added thereto, TiO2 powder prepared in advance is mixed with vanadium or an aqueous solution containing vanadium and phosphorus.
A slurry is formed by dispersing it in an acidic aqueous solution or a thermally decomposable organic medium.

The catalyst slurry obtained in this way was prepared in advance at 150~
It is sprayed onto an inert carrier heated to 400°C, and then heated to 300-600°C, preferably 400-50°C.
The finished catalyst is obtained by calcining in air at a temperature of 0°C for 1 to 10 hours.

Alternatively, TiO2 powder and a compound containing other catalyst components may be mixed and calcined in advance, and the resulting catalyst powder may be made into a slurry liquid and this liquid may be applied to a carrier by spraying or concentrating it. It is possible to obtain a desired catalyst, and a method of supporting a catalyst powder on a carrier using a ball mill can also be adopted.

The composition of the exhaust gas to be treated using the catalyst of the present invention is industrial exhaust gas with a high sulfur oxide content, usually 10 to 2500 ppm of sulfur oxides and 1 to 20% of oxygen.
, carbon dioxide gas 1-15%, water vapor 5-15% 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.

For example, it is possible to treat NOx-containing exhaust gas that does not contain sulfur oxides.

Processing conditions still vary depending on the type and properties of the exhaust gas, but first, the amount of ammonia (NH3) added is
0.5 to 3 parts (molar ratio) per part A molar ratio of around 1:1 to NOx, which is slightly in excess of the equivalent amount, is particularly preferred.

This is because care must be taken not to discharge too much excess NH3 as an unreacted component.

Next, the reaction temperature is 200-400℃, especially 230-35℃.
0°C is preferable, and the space velocity is 1000 to 50000 hr.
-1, particularly in the range of 3000 to 30000 hr-1.

The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 Titanium oxide (TiO2) powder was obtained by the following method.

5,700 g of titanium tetrachloride (TiCl4) was gradually dropped into water to make a 60% aqueous solution, and 2,940 g of sulfuric acid was added to this aqueous solution.
was added under stirring.

On the other hand, prepare a saturated aqueous solution containing 3940 g of ammonium sulfate heated to 100°C, and add this saturated aqueous solution to the TiC
Titanium ammonium sulfate ((NH4)2S
O4.TiOSO4.H20] was precipitated.

This precipitate was separated by filtration and calcined at 500°C for 10 hours.
Further, the titanium ammonium sulfate was thermally decomposed by firing at 700°C for 10 hours, resulting in 2300g of Ti0.
2 powders were obtained.

According to the BET method, the surface area of this TiO2 is 34.4 m2
/g.

A catalyst slurry liquid was prepared by adding 50 g of the thus obtained Ti(h) powder to 150 cc of an oxalic acid aqueous solution containing 15 g of ammonium metavanadate (NH4VO3).

On the other hand, a 4 mmφ spherical silicon carbide (Si
C) Put 100 cc of carrier (surface area 1 m2/g or less), heat it to 250-300°C, and spray the above catalyst slurry while rotating the furnace to support the catalyst component, and then calcinate in air at 450°C for 6 hours. A completed catalyst was obtained.

As a result of fluorescent X-ray analysis, this catalyst contained 14.7 g of TiO2 and 53.3 g of V2O per 100 cc of carrier.

The amount supported was 16% by weight based on the carrier.

Example 2 Norton SA5218 MacroBoat Spherical 4 as carrier
mmφ support (main component α-Al2O386%SiO212
%, surface area 1 m2/g or less) A catalyst was prepared in accordance with the method of Example 1 except that 100 cc was used.

TiO222.4g, V2O55.0g per 100cc of carrier.
0g was supported.

The amount supported was 23% by weight based on the carrier.

Example 3 Crushed α-Al2O3 (with an average particle size of 3 to 5 mm) was used as a carrier.
The catalyst was prepared according to the method of Example 1 except that 100cc of carrier (surface area of 1 m2/g or less) was used.
28.5 g of TiO and 51.9 g of V2O were supported per c.

The amount supported was 8.7% by weight based on the carrier.

Example 4 A catalyst slurry liquid was prepared by adding 65 g of anatabi-type Ti (h powder) with a surface area of 11 m2/g and 20 g of 85% phosphoric acid to 160 cc of an oxalic acid aqueous solution containing 15 g of ammonium metavanadate. SiC used
A catalyst was prepared according to the baking support method of Example 1 using 100 cc of carrier.

Per 100cc of carrier, TiO213.5g, V2O52
．． 9 g and 2.8 g of P20 were supported.

The amount supported was 17.0% by weight based on the carrier.

Example 5 30 g of the anatase-type TiO2 powder used in Example 4 and 20 g of the TiO2 powder used in Example 1 were mixed and added to 150 cc of an oxalic acid acidic aqueous solution containing 15 mm of ammonium metavanadate to prepare a catalyst slurry liquid. .

Using 100 cc of the SA5218 carrier used in Example 2, a catalyst was prepared according to the baking-support method of Example 1.

19.5 g of Ti0, 54.5 g of V2O per 100 cc of carrier.
69 was carried.

The amount supported was 20.0% by weight based on the carrier.

Example 6 200 g of Ti02 powder used in Example 1, 52 g of ammonium metavanadate, ammonium phosphate ((NH
4) Mix 57g of 3・P04・3H20 and heat to 450℃
The powder was fired for 2 hours to obtain 260 g of catalyst powder. This powder was rotated for 2 hours in a ball mill (100 rpm) together with 200 cc of the SiC carrier used in Example 1 to support the catalyst powder on the carrier. It was baked at ℃ for 6 hours.

The catalyst components were 100 cc of carrier, Ti (h26.6, P
, V2055.39XP2052.79 was carried.

The amount supported was 31.0% by weight based on the carrier.

Comparative Example 1 Hydrochloric acid acidic aqueous solution 6 containing 433 g of titanium tetrachloride TiCl
Add 100cc of 4mmφ spherical activated alumina carrier to 0cc, thoroughly impregnate it, concentrate to dryness, and heat at 450℃ for 2 hours.
60 cc of an oxalic acid acidic aqueous solution containing 4.1 g of ammonium metavanadate
was added thereto, the vanadium component was impregnated and concentrated to dryness to support it, and the mixture was calcined at 450° C. for 6 hours.

This product contains 13.3 g of TiO2 and V per 100 cc of carrier.
The carrier contained 53.0 g of 2O, and analysis results using an X-ray microanalyzer showed that both components were impregnated and supported up to the center of the carrier.

The amount supported was 25% by weight based on the carrier.

Comparative Example 2 A catalyst containing no TiO2, that is, only a V2O5 component, was added to the catalyst of Comparative Example 1 at a concentration of 3% per 100cc of activated alumina carrier.
．． A catalyst containing 0 g was prepared.

The amount supported was 4.7% by weight based on the carrier.

Example 7 For each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 and 2, a desktop activity test was conducted in the following manner to compare the initial activities.

15 cc of each catalyst was filled in a stainless steel reaction tube with an inner diameter of 20 mm immersed in a molten salt bath, and a gas of the composition shown in Table 1 below, which was made by adding ammonia to synthesis gas similar to boiler exhaust gas, was supplied at 2.5 l/min. Flow velocity (space velocity 10,000 h
r-1) into the catalyst layer, and the reaction temperature and NOx reduction rate (
Purification rate (%) was determined.

For the NOx analysis, a Chemilumi CLD7S model manufactured by Yanagimoto Co., Ltd. was used.

The results observed are shown in Table 2.

When compared with the catalyst of Comparative Example 2, which represents a conventional catalyst, the catalyst of the present invention is found to have approximately the same level of initial NOx purification rate.

(However, it will be clear from the description below that there is a large difference in durability.

) Example 8 Each of the catalysts obtained in Examples 1 to 6 and Comparative Examples 1 and 2 was subjected to a life durability test using actual gas in the following manner.

45 cc of each catalyst was filled into a 28 mm stainless steel reaction tube immersed in a molten salt bath, and a portion of the boiler exhaust gas was introduced.

Most of the dust entrained in the exhaust gas was removed using an alundum packed bed and a glass wool layer, and then introduced into the catalyst bed.

The average composition of this boiler exhaust gas is NOx 300ppm
, SOx 1400ppm, 02 3.5% by volume, CO
213.5% by volume, 14% by volume of H20, and the balance nitrogen gas, to which 300p of ammonia was added.
pm was added and subjected to contact reaction.

Space velocity (SV) is 10000 hr-1, reaction temperature is 3
The reaction was carried out at a temperature of 30°C, and the results shown in Table 3 were obtained.

As is clear from Table 3, the catalyst of the present invention showed almost no deterioration in activity even after 2000 hours, and in particular, the catalysts containing a phosphorus component in Examples 4 and 6 tended to have a more stable life. On the other hand, it was found that the activity of the catalysts of Comparative Examples 1 and 2 deteriorated significantly.

When the catalyst of Comparative Example 2 was extracted and analyzed, an accumulation of sulfur content was observed, and the results of X-ray diffraction showed the presence of aluminum sulfate, and changes in the pore distribution of the catalyst, especially a decrease in micropores, were observed. Ta.

Example 9 The SO oxidation ability of the catalysts of Examples 1, 2, and 6 and Comparative Example 2 was measured.

That is, from the synthetic exhaust gas composition shown in Example 7, NO and NH3 were removed, SO2 800ppm, O
24% CO2, 10% H2, 10% H2, and the balance N2 are introduced into the catalyst layer, and the S in the inlet gas and outlet gas is
The concentration of O2 was measured and the conversion of SO2 was determined, and the results obtained are shown in Table 4.

From the results shown in the table above, it was found that the conversion rate of SO2, that is, the ability to oxidize to SO3, of the catalyst of the present invention was extremely low, and in particular, the addition of a phosphorus component had the effect of further suppressing the ability to oxidize to SO3.

Example 10 Example 7 Among the synthetic gases shown in Table 1, SO2 was 80%
A desktop activity test was conducted on the catalysts of Examples 1, 2, 3, and 6 using gases with the same composition except that the concentration was changed from 0 ppm to 100 ppm, and the results were similar to those shown in Table 2. I got it.

That is, it has been found that the catalyst of the present invention has high NOx removal performance even for NOx-containing gases with low sulfur content.

Example 11 170 g of the TiO2 powder used in Example 1 and 39 g of ammonium metavanadate were mixed and calcined at 450° C. for 2 hours to obtain 200 g of catalyst powder.

A catalyst slurry liquid was prepared by adding 30Occ of water to this powder, and a mullite lattice carrier (surface area of 1 m2/g or less) was prepared by adding 30Occ of water.
After being immersed for 10 minutes in the catalyst slurry liquid obtained in an amount of 0 cc, it was dried and then calcined in air at 450° C. for 6 hours to obtain a completed catalyst.

TiO29.4g, V2O51.6 per 100cc of carrier
g was supported.

The wandering amount was 25% by weight based on the carrier.

Space velocity 100 according to Example 7 for the observed catalyst
When the NOx reduction rate was measured at 00Hr-1, it was found to be 250
88%, 92%, 96%, 93%, and 90% at each reaction temperature of 300°C, 325°C, 350°C, and 400°C.

Next, the conversion rate of SO2 was measured according to Example 9 and found to be 3.1%.

Example 12 170 g of the TiCh powder used in Example 1 and 39 g of ammonium metavanadate were mixed and calcined at 450° C. for 2 hours to obtain 200 g of catalyst powder.

A catalyst slurry liquid was prepared by adding 300 cc of water to this powder, and a magnesium silicate corrugated carrier (surface area 1 m2) was prepared.
/g or less, a carrier made of magnesium silicate fibers molded into a corrugated shape and integrated) 100cc was immersed in the obtained catalyst slurry for 10 minutes, dried, and calcined in air at 450°C for 6 hours to obtain the finished catalyst. I got it.

Ti029.4g, V2051.6 per 100cc of carrier
g was supported.

The amount supported was 35% by weight based on the carrier.

The space velocity of the obtained catalyst was 100 according to Example 7.
When the NOx reduction rate was measured at 00Hr-1, it was found to be 250
88%, 92%, 96%, 93%, and 90% at each reaction temperature of 300°C, 325°C, 350°C, and 400°C.

Next, the conversion rate of SO2 was measured according to Example 9 and found to be 3.1%.

Claims (1)

[Claims] 1 As a catalyst that selectively reduces nitrogen oxides by adding ammonia to a harmful gas containing nitrogen oxides and catalytically reacting the mixed gas, the surface area according to the BET method is 10 m2/g or less. A catalytic material consisting of titanium and vanadium, or phosphorus added thereto, on a low surface area inert support is present in an amount of 3 to 50% by weight based on the support.
The titanium component is supported in the range of B
A catalyst composition for removing nitrogen oxides, characterized in that it is introduced as titanium oxide having a surface area of at least 10 m2/g by the ET method.