JPH09155190A - Catalyst for removing nitrogen oxides in exhaust gas, production thereof and method for removing nitrogen oxides in exhaust gas using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove NOx within a low temp. region of 150-300 deg.C. SOLUTION: In a method for producing a catalyst removing nitrogen oxides by catalytically reducing nitrogen oxides in exhaust gas by ammonia, titanium oxide containing a sulfate radical is preliminarily baked at 500-700 deg.C or immersed in an alkali soln. to be washed therewith to reduce the content of the sulfate radical to 0.1wt.% or less and this titanium oxide is kneaded and/or impregnated with manganese nitrate and, further, the treated titanium oxide is baked at 200-450 deg.C to support MnO2 on a titanium oxide carrier as an active component to obtain a denitration catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, a method for producing the same and a method for removing nitrogen oxides in exhaust gas using the same, and particularly to a low exhaust gas temperature of 150 to 300 ° C. NOx in exhaust gas efficiently in the region
TECHNICAL FIELD The present invention relates to a catalyst for removing nitrogen oxides in exhaust gas, which can be catalytically reduced with ammonia, a method for producing the same, and a method for removing nitrogen oxides in 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 substance of photochemical smog and acid rain, and as an effective removal method, ammonia (NH ₃ ) is reduced. The flue gas denitration method by selective reduction as an agent is widely used. Particularly in recent years, there is an increasing need for exhaust gas denitration at 150 to 300 ° C., which has a lower temperature than conventional business boiler exhaust gases such as combustion exhaust gases from waste incinerators and waste heat recovery boiler exhaust gases. Catalysts that are highly active in such a low temperature range include manganese (Mn), chromium (C
r), vanadium (V), and catalysts in which these are combined are known. Among them, Mn is particularly excellent in low-temperature activity (JP-A-50-131848).

[0003]

However, the above-mentioned prior art does not give sufficient consideration to the inhibition of low temperature activity expression by the components contained in the catalyst other than Mn, and points to be improved. There were many One of them is how to support Mn as an active ingredient. For example, when manganese sulfate is used as a raw material for Mn, manganese sulfate is stable up to 850 ° C., so that manganese takes the form of manganese sulfate in the catalyst. However, manganese is almost inactive with respect to denitration with sulfate, so denitration activity cannot be obtained. When manganese nitrate is used, various forms of manganese oxides (MnO, MnO, etc.) are used depending on the conditions at the time of catalyst calcination.
₂ , Mn ₂ O ₃ , Mn ₃ O _{4 and the} like) are formed, and there is a problem that a highly active catalyst may be obtained, or conversely, there may be almost no activity.

The object of the present invention is to elucidate the mechanism of manifestation of the activity of the manganese catalyst and solve the problems of the above-mentioned prior art on the basis thereof, whereby NOx can be efficiently produced in the exhaust gas temperature range as low as 150 to 300 ° C. An object of the present invention is to provide a catalyst for removing nitrogen oxides in exhaust gas, a method for producing the same, and a method for removing nitrogen oxides in exhaust gas using the catalyst.

[0005]

The invention claimed in this application to achieve the above object is as follows. (1) In a catalyst for catalytically reducing nitrogen oxides in exhaust gas with ammonia, titanium oxide having a sulfate content of 0.1% by weight or less is used as a carrier, and manganese is kneaded with nitrate and / or Impregnated and loaded, 20
A catalyst for removing nitrogen oxides in exhaust gas, which is calcined at 0 to 450 ° C. (2) A method for removing nitrogen oxides in exhaust gas, which comprises catalytically reducing nitrogen oxides in exhaust gas with ammonia in a temperature range of 150 to 300 ° C. using the catalyst according to (1).

(3) In the method of catalytic reduction removal of nitrogen oxides in exhaust gas with ammonia injected at a temperature of 150 to 300 ° C. in the presence of a denitration catalyst, the content of sulfate group is 0.1% by weight or less. Manganese M on titanium oxide carrier
A catalyst supported in the form of nO ₂ is arranged in the upstream region of the NOx removal catalyst, whereby a part of NO in the exhaust gas is converted into NO ₂ , and then ammonia is injected to NOx in the exhaust gas on the NOx removal catalyst. A method for removing nitrogen oxides in exhaust gas, which comprises catalytically reducing. (4) In the method for producing a catalyst in which nitrogen oxides in exhaust gas are catalytically reduced and removed with ammonia, titanium oxide containing a sulfate group is preliminarily calcined in a temperature range of 500 to 700 ° C., or an alkaline solution is used. The content of sulfate in the titanium oxide is adjusted to 0.1% by weight or less by immersing in manganese and washing, and manganese is kneaded and / or impregnated with nitrate.
A method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises calcination at 0 ° C.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst for removing nitrogen oxides in exhaust gas according to the present invention has (1) the content of sulfate radicals of 0.1 wt%
The following titania (TiO ₂ ) is used as a carrier, (2) a nitrate is used as a manganese salt to be supported as an active ingredient, and (3) firing is performed in a temperature range of 200 to 450 ° C.

[0008] That is, the TiO ₂ content of less 0.1 wt% of sulfate group, a TiO ₂ of the anatase type and / or rutile type, TiO ₂ and 500 ° C. or higher produced by sulfuric acid method, preferably 550-700 ° C
It means that the content of sulfate radicals is reduced by firing within the temperature range of 1, or that residual sulfate radicals are washed and removed in an aqueous solution such as NH ₃ water. Further, manganese nitrate may be kneaded together with the TiO ₂ using a kneader, or a molded body of TiO ₂ may be previously impregnated with an aqueous solution of manganese nitrate. The supported amount of manganese is not particularly limited, but is 1 to Ti.
Good results are obtained when used within the range of 20 atom%. If it is 1 atom% or less, sufficient activity cannot be obtained, and if it is more than 20 atom%, problems such as pore clogging occur, which is not preferable.

Further, the calcination temperature of the catalyst is particularly important,
It is in the range of 00 to 450 ° C, preferably 250 to 400 ° C. This is because the morphology of the Mn oxide in the catalyst described later is extremely closely related to the low temperature activity of the catalyst. As a result of investigating the mechanism of low temperature activity of the catalyst, the present inventors have found that the low temperature activity is closely related to the catalyst's activity of oxidizing NO in exhaust gas to NO ₂ . That is, when NO and NO ₂ coexist in the exhaust gas, the reaction (1) that is much faster than the normal denitration reaction (2) proceeds, but the reaction rate of (1) is known to be faster at a low temperature of 300 ° C. or lower. ing. Therefore, if the catalyst has the function of oxidizing NO in exhaust gas to NO ₂ together with the denitration function, a part of NO becomes NO _{2 according} to the following reaction formula (3) on the catalyst, Then NO and NO
₂ becomes a state of coexistence, and the faster denitration reaction (1) equation (1) progresses at the same time as the reaction of equation (2).
High denitration activity can be obtained even at a low temperature of 300 ° C.

NOx removal reaction NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (1) formula NO + NH ₃ +1/4 O ₂ → N ₂ +3/2 H ₂ O (2) formula NO oxidation reaction NO + 1/2 O ₂ → NO ₂ (3) Formula Using this as an index, the oxidation activity of NO of various manganese catalysts to NO ₂ was examined. As shown in Table 1, when manganese sulfates and organic acid salts were used as manganese raw materials, NO Was found to be inactive in the oxidation of NO to NO ₂ .

[0011]

[Table 1]

As described above, manganese has various structures depending on the starting material, the method for preparing the same, and the post-treatment conditions such as heating, and the chemical activity thereof varies accordingly. Therefore, in the process of preparing the catalyst, measures are taken to prevent the active component manganese from being sulfated and reduce the production of MnO, which is a thermal decomposition product of manganese oxalate, to become active MnO _2. It is important that a highly active manganese catalyst can be obtained only by paying attention to this and preparing the catalyst. That is, in the present invention, titania having a low sulfate content is used as a carrier to prevent manganese from being sulfated, and manganese nitrate is used as a raw material for manganese to reduce NO.
It made it easy to generate MnO _2, which is highly active in oxidizing to O ₂ . Further, the firing temperature is 200 to 450 ° C. N
The temperature was selected such that a large amount of MnO ₂ active in the oxidation of O to NO ₂ was produced. The manganese catalyst obtained under such specific conditions can obtain a highly active catalyst even in the exhaust gas temperature range of 150 to 300 ° C.

The present invention will be described in detail below with reference to specific examples. Example 1 Titanium oxide (manufactured by Rhone Poulenc, sulfate content 0.67)
100 wt%) was calcined at 600 ° C. for 2 hours in the air.
When the sulfate content in the titanium oxide after calcination was examined using a fluorescent X-ray analyzer, it was below the detection limit of 0.01 wt%.

[0014] manganese nitrate _{(Mn (NO 3) 2 ·} 6H
A catalyst solution was prepared by dissolving 38.8 g of ₂ O) in 30 g of water, 100 g of the above titanium oxide was added thereto, and the mixture was evaporated to dryness on a sand bath at 100 ° C. or higher. This was dried at 150 ° C. for 2 hours and then calcined in air at 400 ° C. for 2 hours. The obtained catalyst was crushed in a mortar and molded into pellets with a hydraulic press at a pressure of 3 ton / cm ² , and further crushed to obtain a catalyst of 10 to 20 mesh.

The composition at this time was Mn / Ti = 1/9 (atomic ratio). Example 2 39.9 g of manganese nitrate of Example 1 was replaced with 19.9 g, and thereafter a catalyst was similarly prepared. The composition at this time is Mn
/ Ti = 5/95 (atomic ratio). Example 3 200 g of titanium oxide (TiO ₂ , manufactured by Rhone Poulenc, content of sulfate group: 0.67 wt%) was added to 1 liter of 10% ammonia water, and left overnight with stirring at 80 ° C. This was filtered, washed with water, and dried at 150 ° C. for 5 hours. When the sulfate content of the obtained TiO ₂ was examined by using a fluorescent X-ray analyzer, it was 0.05 wt%. A catalyst was prepared in the same manner as in Example 1 except that 100 g of TiO ₂ thus obtained was used. The composition at this time is M
It was n / Ti = 1/9 (atomic ratio).

Example 4 Titanium oxide (manufactured by Rhone Poulenc, sulfate content 0.67)
150 wt%) was fired at 600 ° C. for 2 hours in the atmosphere.
When the sulfate content in the titanium oxide after calcination was examined using a fluorescent X-ray analyzer, it was below the detection limit of 0.01 wt%. This was molded into pellets with a hydraulic press at a pressure of 3 ton / cm ² and further crushed for 10 to 20
It was a mesh.

[0017] manganese nitrate _{(Mn (NO 3) 2 ·} 6H
A catalyst solution was prepared by dissolving 39.9 g of ₂ O) in 200 g of water, and 100 g of the above-prepared titanium oxide was added and impregnated. After drying this at 150 ° C for 2 hours, it is dried in air 4
The catalyst was obtained by calcining at 00 ° C. for 2 hours. The composition at this time was Mn / Ti = 1/9 (atomic ratio). Comparative Example 1 TiO ₂ (Rhône-Poulenc Ltd. TiO _2, sulfate ion content 0.67wt%) with untreated the 100 g, later was prepared in the same manner as catalyst as in Example 1. Comparative Example 2 The manganese nitrate of Example 1 was replaced with manganese sulfate (MnSO ₄ ·.
5H ₂ O) was replaced with 33.5 g, and thereafter a catalyst was prepared in the same manner. The composition at this time was Mn / Ti = 1/9 (atomic ratio). Comparative Example 3 The manganese nitrate of Example 1 was replaced with manganese oxalate (MnC ₂
(O ₄ .2H ₂ O) was changed to 24.9 g, and thereafter a catalyst was prepared in the same manner. The composition at this time was Mn / Ti = 1/9 (atomic ratio).

Comparative Example 4 Instead of manganese nitrate of Example 1, manganese nitrate (Mn
_{(NO 3) 2 · 6H 2} O) 42.2g and ammonium metavanadate (NH ₄ VO ₃₎ and 8.6 g, after A catalyst was prepared in the same manner. The composition at this time is Mn / V / Ti = 10.
It was / 5/85 (atomic ratio). Comparative Examples 5 to 7 TiO ₂ of Example 1 was replaced with SiO ₂ (microcomputer F), Al ₂ O ₃ , and mordenite (TSZ6 manufactured by Tosoh Corporation).
Instead of 50), a catalyst was prepared in the same manner as in Example 1. Experimental Example 1 A reactor was charged with 3 ml of the catalysts of Examples 1 to 4 and Comparative Examples 1 to 7, and the concentrations of NOx and NO detected at the inlet and the outlet of the reactor were measured under the conditions shown in Table 2. NO of NO ₂
The oxidization rate was measured.

[0019]

[Table 2] The NO ₂ conversion rate is defined as follows.

[0020]

(Equation 1)

Further, Experimental Examples 1 to 4 and Comparative Examples 1 to 7
4.5 ml of the above catalyst was charged into a reactor, and under the conditions of Table 2, ammonia was added in 1.2 times mol of NOx, and the denitration rate was measured. The results are summarized in Table 3.

[0022]

[Table 3] TiO ₂ *: TiO ₂ is baked at 600 ° C, TiO ₂ **: TiO ₂ is washed with NH ₃ water.

As is clear from the table, the catalysts of the examples according to the present invention have an NO to NO ₂ oxidation rate of 10 to 20%, and a denitration rate of 59 to 70%, which is a high denitration activity that has never been seen in the past. Is shown. In contrast, the catalyst of the comparative example is NO
There is almost no oxidation activity to _2, and the denitrification rate is low. Thus, it can be seen that the manganese catalyst obtained by the preparation method according to the present invention is excellent. Examples 5 and 6 Catalysts were obtained in the same manner as in Example 1 except that the manganese-supporting TiO ₂ of Example 1 was fired at temperatures of 250 and 450 ° C., respectively. Comparative Examples 8 and 9 Catalysts were obtained in the same manner as in Example 1 except that the manganese-supporting TiO ₂ of Example 1 was fired at temperatures of 150 and 500 ° C., respectively.

Using the catalysts of Examples 5 and 6 and Comparative Examples 8 and 9, the same tests as in Experimental Example 1 were carried out to measure the NO oxidation activity and the denitration activity. The results are summarized in Table 4.

[0025]

[Table 4] As is clear from the table, when the firing temperature after supporting manganese is 250 to 450 ° C., which is the range of the present invention, high NO oxidation activity and denitration activity are expressed, but temperatures outside this range are too high. Even if it is too low, high activity cannot be obtained. As described above, it is understood that the catalyst of the present invention is an excellent catalyst that can highly activate manganese by improving the conventional problems. Example 7 Ten 1400 twisted threads of E-glass fiber having a fiber diameter of 9 μm
Titania 40 on a net woven with book / inch roughness
%, Silica sol 20%, polyvinyl alcohol 1% slurry was impregnated and dried at 150 ° C. to give rigidity to obtain a catalyst substrate.

Separately from this, 20 kg of TiO ₂ and 7.98 kg of manganese nitrate were added to silica / alumina type inorganic fiber 4.
2 kg and 11 kg of water were added and kneaded with a kneader to obtain a catalyst paste. The paste catalyst mixture prepared between the two base materials was placed and passed through a pressure roller to press the catalyst between the stitches and the surface of the base material to obtain a plate-like catalyst having a thickness of about 1 mm. The obtained catalyst was dried at 150 ° C. for 2 hours and then calcined in the air at 350 ° C. for 2 hours. Other Experimental Examples The plate-shaped catalyst of Example 7 was arranged at a 4 mm pitch in front of the denitration catalyst layer of the small-sized reactor having the system of FIG. 1, and the gas having the composition of Table 2 was flowed to the NOx concentration at the inlet and the outlet. Was measured to examine the denitration rate. At this time, ammonia 5 which is a reducing agent for denitration
Was injected between the catalyst layer 1 and the denitration catalyst layer 2 of Example 7 at a ratio of 1.2 mol with respect to NOx. Ratio = 95/4 /
(5, thickness 1 mm) plate catalysts arranged at a pitch of 4 mm,
The conditions shown in Table 5 were maintained. Further, gas was sampled between the catalyst layer and the denitration catalyst layer of Example 7 to measure NOx and NO concentrations, and the oxidation rate of NO to NO ₂ was examined.

[0027]

[Table 5] As a result, NO at the catalyst layer outlet of Example 7 in FIG.
Of NO to NO ₂ was 28%, and the NOx removal rate measured at the outlet of the apparatus was 83%. This was extremely high in comparison with the denitration ratio of 66% when the catalyst of Example 7 was removed and the same test was performed using only the denitration catalyst. From these results, it is shown that the catalyst of the present invention has an activity of oxidizing NO to NO _2, and therefore can be used not only as a denitration catalyst but also as an NO to NO ₂ oxidation catalyst.

[0028]

According to the present invention, the most highly active manganese catalyst can be obtained, and by using this catalyst, high denitration performance can be obtained even in a low temperature range of 150 to 300 ° C. As a result, it becomes possible to denitrate the low-temperature exhaust gas such as exhaust gas from a refuse incinerator, which has been in increasing demand in recent years, without preheating, and it is possible to realize exhaust gas treatment that is extremely simple and has a low operating cost.

Further, by placing this catalyst in the upstream of the denitration catalyst, the low temperature activity of the conventional denitration catalyst can be greatly improved, which leads to the expansion of the application range of the ammonia reduction flue gas denitration method.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of the present invention.

[Explanation of symbols]

1 ... Catalyst of Example 7 of the present invention, 2 ... Ti / W / V denitration catalyst, 3 ... Flue, 4 ... NOx generation source (eg: refuse incinerator), 5 ... Ammonia.

Claims (4)

[Claims] 1. A catalyst for catalytic reduction removal of nitrogen oxides in exhaust gas with ammonia, wherein titanium oxide having a sulfate content of 0.1% by weight or less is used as a carrier, and manganese is kneaded with nitrate and And / or impregnated and supported,
A catalyst for removing nitrogen oxides in exhaust gas, which is obtained by firing at 200 to 450 ° C. 2. The catalyst according to claim 1, which is used in the range of 150 to 3
A method for removing nitrogen oxides in exhaust gas, which comprises catalytically reducing nitrogen oxides in exhaust gas with ammonia in a temperature range of 00 ° C. 3. A method for catalytically reducing nitrogen oxides in exhaust gas by using ammonia injected at a temperature of 150 to 300 ° C. in the presence of a denitration catalyst, and titanium containing 0.1% by weight or less of sulfate group. Manganese is added to the oxide carrier as Mn.
A catalyst supported in the form of O ₂ is arranged in the upstream region of the NOx removal catalyst, whereby a part of NO in the exhaust gas is converted into NO ₂ , and then ammonia is injected to NOx in the exhaust gas on the NOx removal catalyst. A method for removing nitrogen oxides in exhaust gas, which comprises catalytically reducing. 4. A method for producing a catalyst for catalytically reducing nitrogen oxides contained in exhaust gas with ammonia, wherein titanium oxide containing sulfate is preliminarily added to 500 to 700.
The sulfate group content of the titanium oxide is adjusted to 0.1% by weight or less by baking in a temperature range of ℃ or by immersing in an alkaline solution and washing, and manganese is kneaded with nitrate and / or Impregnate and then add 20
A method for producing a catalyst for removing nitrogen oxides in exhaust gas, which comprises calcination at 0 to 450 ° C.