JP2506588B2 - Nitrogen oxide removal method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hydrocarbon or oxygen-containing compound to which a small amount of exhaust gas is added, or a hydrocarbon or oxygen-containing compound present in exhaust gas under oxidizing conditions as a whole in the presence of excess oxygen. The present invention relates to a method of contacting a specific catalyst in the presence of a compound to reduce and remove nitrogen oxides in the exhaust gas.

[0002]

2. Description of the Related Art Nitrogen oxides in various exhaust gases (hereinafter referred to as
Since "NOx") is harmful to health and can cause photochemical smog and acid rain, it is desired to develop an effective removal method therefor.

Conventionally, as a method for removing NOx, several methods for reducing NOx in exhaust gas using a catalyst have already been put to practical use. For example, (a) a three-way catalytic method in a gasoline vehicle, and (b) a selective catalytic reduction method using ammonia for exhaust gas from a large facility discharge source such as a boiler. As another proposed method, (c) NOx in exhaust gas using hydrocarbon
As a removal method, there is a method of contacting a gas containing NOx in the presence of hydrocarbon with a hydrophobic zeolite carrying a metal as a catalyst (Japanese Patent Laid-Open No. 63-283727).

[0004]

SUMMARY OF THE INVENTION The method (a) is
The hydrocarbon component and carbon monoxide component contained in the flue gas of an automobile are converted into water and carbon dioxide by a catalyst, and at the same time N
Ox is reduced to nitrogen, so that the amount of oxygen contained in NOx and the amount of oxygen required for oxidizing hydrocarbon components and carbon monoxide are stoichiometrically equal. Combustion needs to be adjusted, and there is a serious problem that it cannot be applied in principle in a system in which excess oxygen exists, such as exhaust gas from a diesel engine or a lean burn gasoline engine.

In the method (b), ammonia is used which is very toxic and which must be handled as a high-pressure gas in many cases. In particular, it is extremely difficult to apply to mobile sources, and it is not economical.

On the other hand, the method (c) is mainly applied to gasoline automobiles, and it is difficult to apply it under the exhaust gas conditions of diesel engines due to catalyst poisoning by sulfur oxides and the catalyst under oxygen excess conditions. Has insufficient selectivity and is economically disadvantageous.

The inventors of the present invention have conducted diligent research in order to solve various problems existing in (a) to (c) above, and as a result, the metal oxide treated with the compound containing a sulfate group has oxygen. It was found that the catalyst has high catalytic performance for reducing and removing NOx by hydrocarbons in an excess atmosphere, and already applied for a method for purifying NOx-containing exhaust gas using the catalyst (Japanese Patent Application No. 2-204103). By the way, the above catalyst used in the method of Japanese Patent Application No. 2-204103 exhibits epoch-making performance in terms of reducing and removing ability of nitrogen oxides, but lacks activity at a low temperature of 400 ° C. or lower. ing. Therefore, in the present invention, a catalyst having high activity even at a low temperature of 400 ° C. or lower was developed, and 400 ° C. was obtained by using such a catalyst.
It is an object of the present invention to propose a method capable of removing NOx with high efficiency even at the following low temperatures.

[0008]

Means and Action for Solving the Problems The present inventors have
As a result of extensive studies to achieve the above-mentioned object, it was found that the catalyst used in the above-mentioned NOx purification method of the above-mentioned application, in which vanadium was supported, exhibited extremely high low-temperature activity, and the present invention was developed. .

That is, according to the method for removing nitrogen oxides of the present invention, vanadium is supported on a metal oxide containing a sulfate group in the presence of a hydrocarbon or an oxygen-containing compound in an oxidizing atmosphere containing excess oxygen. The catalyst is brought into contact with an exhaust gas containing NOx, and the catalyst is also brought into contact with the catalyst under the same conditions as described above, and then the exhaust gas is brought into contact with an oxidation catalyst.

Hereinafter, the details of the method of the present invention will be described together with the operation. The catalyst that can be used in the method of the present invention is a metal oxide containing a sulfate group such as titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), iron oxide (Fe ₂ O ₃ ), alumina (Al ₂ O). ₃ ), hafnium oxide (HfO ₂ ), tin oxide (SnO ₂ ), titania-
It is a catalyst in which vanadium is supported on zirconia (TiO ₂ —ZrO ₂ ), silica-alumina (SiO ₂ —Al ₂ O ₃ ), and the like. Here, "containing a sulfate group" means containing about 0.1 to 10 wt% of sulfur in the form of a sulfate group (SO ₄ ). Regarding that a metal oxide having such a form has a high catalytic activity, The details are given in the above-mentioned specification of the previously filed application.

Taking titanium oxide as an example of the above metal oxide, titanium oxide containing a sulfate group is obtained by bringing amorphous titanium oxide or titanium hydroxide (titanic acid) into contact with a compound containing a sulfate group. After drying, it can be obtained by baking in air at a specific temperature. Specific examples of the compound having a sulfate group include sulfuric acid, ammonium sulfate, and any other compound that produces a sulfate group by a drying treatment after the sulfate group-containing treatment. The concentration of sulfuric acid used for the treatment containing sulfate radicals is usually about 0.01
-10 mol / 1, preferably about 0.1-5 mol / 1
And the concentration of sulfuric acid is about 5 to 5 per amorphous titanium oxide.
Use 20 times the amount. Air firing temperature is about 300-700
C., preferably about 400-600.degree. C., and the firing time is about 1-10 hours. Air firing temperature is about 300 ℃
If the calcination time is less than about 1 hour, free sulfuric acid may not be removed and catalytic active sites may not be formed.
At higher temperatures, the surface area is reduced or the catalytic active sites are destroyed, and even if it is burned for about 10 hours or more, the effect corresponding to it cannot be obtained.

Titanium oxide containing a sulfate group can be obtained by neutralizing an aqueous solution of titanium sulfate (titanium sulfate or titanyl sulfate) with an alkaline aqueous solution or heating and hydrolyzing the resulting precipitate to obtain a precipitate, which is calcined in air. You can also get Ammonia water is usually used as the alkaline aqueous solution. The thermal hydrolysis is performed by heating an aqueous solution of titanium sulfate to 100 to 150 ° C. in an autoclave. Air firing temperature is about 300-800
C., preferably about 400-600.degree. C., and the firing time is about 1-10 hours.

Other metal oxides can be similarly prepared. For example, zirconium oxide containing sulfate is zirconium hydroxide or 400 ° C.
It can be obtained by bringing the amorphous zirconium oxide calcined below into contact with a compound having a sulfate group, drying and then calcining in air at a specific temperature and time. Specific examples of the compound having a sulfate group, the concentration of sulfuric acid, the amount used, the air calcination temperature, and the calcination time at this time are the same as those for titanium oxide.

The method for supporting vanadium on the metal oxide containing sulfate is not particularly limited, and any conventionally known method can be used. For example, in the impregnation method, a metal oxide containing sulfate is impregnated with an aqueous solution of a vanadium compound,
After drying, it can be supported by air calcination. As a compound of vanadium, vanadium chloride (V
Clx: x = 2-4), vanadyl chloride (VOClx: x
= 1 to 3), vanadium sulfate (VSO ₄ ), vanadyl sulfate ((VOSO ₄ ), vanadyl acetyl acetate (V
_{O (CH 2 COCH 2 COCH 3} ) 2), oxalic acid vanadyl _{(VOC 2 O} 4), ammonium metavanadate (NH
₄ VO ₃ ), and the like. Usually, ammonium metavanadate (NH ₄ VO ₃ ) is preferably used, and it is heated to increase the solubility or oxalic acid is added to form a uniform aqueous solution. The supported amount of vanadium is about 0.5 to 30 w with respect to the metal oxide containing a sulfate group in terms of metal.
t%, preferably about 1-10 wt%. About 0.5w
If it is less than t%, there is no supporting effect, and if it is more than about 30 wt%, it may cover the sulfate group-containing metal oxide as a carrier, and the concerted effect of the sulfate group-containing metal oxide and vanadium may not be exhibited. There is The air calcination temperature is about 300 to 800 ° C, preferably about 400 to 600 ° C, and the calcination time is about 1 to 10 hours. The supported vanadium acts on the active sites of sulfate-containing metal oxides such as sulfate-containing titanium oxide and sulfate-containing zirconium oxide, which are carriers, and has a function of dramatically improving NOx reduction activity at low temperatures. .

The above catalyst can be used in the form of powder, granules, pellets, honeycomb, or any other shape, and its shape and structure are not particularly limited. Further, when the catalyst is molded and used, a binder which is usually used at the time of molding, that is, silica sol, polyvinyl alcohol or the like, or a lubricant, that is, graphite, wax, fatty acid salt, carbon wax or the like can be used.

Examples of NOx-containing gas to be treated by the method of the present invention include diesel engine exhaust gas from diesel vehicles and stationary diesel engines, gasoline engine exhaust gas from gasoline vehicles, lean burn gasoline engine exhaust gas, nitric acid manufacturing plants, Exhaust gas from various combustion facilities can be used.

The removal of NOx from the exhaust gas is carried out by using the catalyst described in detail above and bringing the exhaust gas into contact with the catalyst in the presence of hydrocarbons or oxygen-containing compounds in an oxidizing atmosphere. Here, the oxidizing atmosphere is used to completely oxidize carbon monoxide, hydrogen and hydrocarbons contained in the exhaust gas and reducing substances such as hydrocarbons or oxygen-containing compounds added according to the method of the present invention. In the case of exhaust gas emitted from an internal combustion engine such as an automobile, the air ratio is large ( The atmosphere is in a lean region, and the excess oxygen ratio is usually about 20 to 2
It is about 00%. In this oxidizing atmosphere, the catalyst preferentially promotes the reaction between hydrocarbons and the like and NOx over the reaction between the hydrocarbons and the like and oxygen, and reduces and removes NOx. The catalyst in the method of the present invention works well in an oxidizing atmosphere, but the reducing activity of NOx may decrease in a reducing atmosphere. Therefore, it is preferable to carry out the reaction in an oxidizing atmosphere.

As the reducing substance for reducing and removing the hydrocarbons or oxygen-containing compounds, that is, NOx, to be present, particulates which are incomplete combustion products of hydrocarbons and fuels remaining in the exhaust gas may be used. If the amount is less than the amount required to accelerate the reaction, it is necessary to add hydrocarbons or oxygen-containing compounds from the outside. The amount of hydrocarbons or oxygen-containing compounds to be present is not particularly limited, and in some cases, for example, when the required NOx removal rate is low, it may be less than the theoretical amount required for reducing and removing NOx. However, since the reduction reaction proceeds more than the required theoretical amount, it is generally preferable to add in excess. Usually, the amount of hydrocarbons or oxygen-containing compounds is about 20 to the theoretical amount required for NOx reduction.
It is present in a 2,000% excess, preferably about 30-1,500% excess.

Here, the necessary theoretical amount of hydrocarbons or oxygen-containing compounds means that oxygen exists in the reaction system.
In the method of the present invention, it is defined as the amount of hydrocarbons or oxygen-containing compounds required for reducing and removing nitrogen dioxide (NO ₂ ). For example, propane is used as the hydrocarbons at 1,000 ppm. Nitric oxide (N
The theoretical amount of propane when reducing O) in the presence of oxygen is 2
It becomes 00 ppm. Generally, depending on the amount of NOx in the exhaust gas, the amount of hydrocarbons or oxygen-containing compounds to be present is about 50 to 10,000 ppm in terms of methane.

In the method of the present invention, as the reducing substance for reducing NOx by the above-mentioned catalyst, any substance can be used as long as it is a carbon-containing substance such as a flammable organic compound. Compounds such as nitrogen, sulfur, and halogen have many problems such as price, secondary generation of harmful substances, and damage to the catalyst, and solid substances such as carbon black and coal are supplied to the catalyst layer and the catalyst. Generally, it is not preferable from the viewpoint of contact with, and hydrocarbons or oxygen-containing compounds are preferable. From the viewpoint of supply to the catalyst layer, a gas or liquid is preferable, and from the viewpoint of reaction, a substance that vaporizes at the reaction temperature is particularly preferable.

Specific examples of the hydrocarbons in the method of the present invention include gaseous hydrocarbons such as methane, ethane, ethylene, propane, propylene, butane and butylene, and liquid hydrocarbons such as pentane. Examples include single hydrocarbons such as hexane, octane, heptane, octene, benzene, toluene, xylene, and mineral oil hydrocarbon oils such as gasoline, kerosene, light oil, and heavy oil. Also,
The oxygen-containing compound in the method of the present invention means an oxygen-containing organic compound, and includes alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol and octyl alcohol, ethers such as dimethyl ether, ethyl ether and propyl ether, methyl acetate and acetic acid. ethyl,
Examples thereof include esters such as fats and oils, and oxygen-containing organic compounds such as ketones such as acetone and methyl ethyl ketone. These hydrocarbons or oxygen-containing compounds may be used alone or in combination of two or more.

Unburned or incompletely burned products such as fuel existing in the exhaust gas, that is, hydrocarbons and particulates are also effective as reducing agents, and these are also included in the hydrocarbons in the method of the present invention. Be done. From this, it can be said that the catalyst in the method of the present invention also has a function as a catalyst for reducing / removing hydrocarbons and particulates in exhaust gas.

The reaction is carried out by preparing a reactor in which the above catalyst is arranged, allowing hydrocarbons or oxygen-containing compounds to exist in an oxidizing atmosphere, and passing NOx-containing exhaust gas. The optimum reaction temperature at this time varies depending on the type of the catalyst and the hydrocarbons or oxygen-containing compounds. However, a temperature close to the temperature of the exhaust gas is preferable because heating equipment for the exhaust gas is not required.
C., especially in the range of about 200-600.degree. The reaction pressure is not particularly limited, and the reaction proceeds under pressure or reduced pressure, but it is convenient to introduce the exhaust gas into the catalyst layer at a normal exhaust pressure to proceed the reaction. Space velocity depends on the type of catalyst,
It is determined by other reaction conditions, the required NOx removal rate, etc. and is not particularly limited, but is generally about 100 to 100,000 Hr ⁻¹ ,
It is preferably in the range of about 500 to 20,000 Hr ^-1 . In the method of the present invention, when treating exhaust gas from an internal combustion engine, it is preferable that the catalyst be disposed downstream of the exhaust manifold.

When the exhaust gas is treated by the method of the present invention, depending on the treatment conditions, incomplete combustion products such as unburned hydrocarbons and carbon monoxide that cause pollution are discharged into the treated gas. There is a case. As a countermeasure in such a case, a method in which the gas treated with the above-mentioned catalyst (hereinafter, referred to as “reduction catalyst”) is brought into contact with the oxidation catalyst can be adopted.

As the oxidation catalyst which can be used in the method of the present invention, generally, any substance can be used as long as it can completely burn the incomplete combustion product, but activated alumina, silica, zirconia and the like can be used. Noble metals such as platinum, palladium and ruthenium, base metal oxides such as lanthanum, cerium, copper, iron and molybdenum, perovskite type crystal structures such as lanthanum trioxide trioxide, lanthanum trioxide trioxide and strontium cobalt trioxide The catalyst components such as these are supported alone or in combination of two or more. The supported amount of these catalyst components is about 0.01 to 2 wt% with respect to the carrier for the noble metal, and about 5 to 70 wt% for the base metal oxide or the like. Of course, it is also possible to use the base metal oxide without supporting it on a carrier. The shape of the oxidation catalyst, the additives added for the purpose of molding, etc. are the same as those in the case of the reduction catalyst,
Various ones can be used.

The use ratio of the above reduction catalyst and oxidation catalyst,
The amount of the catalyst component supported on the oxidation catalyst can be appropriately selected depending on the required performance. Particularly, when the substance to be oxidized and removed is a hydrocarbon intermediate oxide such as carbon monoxide, the reduction catalyst and the oxidation catalyst Although it is possible to use a mixture with a catalyst, it is possible to arrange the reduction catalyst on the exhaust gas upstream side and the oxidation catalyst on the exhaust gas downstream side in general.

In the method of the present invention, as a specific example of purifying exhaust gas using these catalysts, a reactor in which a reduction catalyst is arranged is an exhaust gas introduction section (first stage), and a reactor in which an oxidation catalyst is arranged is an exhaust gas discharge section. The method of arranging in (the latter stage), 1
There is a method of arranging each catalyst in one reactor at a ratio according to the required performance. The ratio of the reduction catalyst (A) to the oxidation catalyst (B) is generally expressed by (A) / (B) and is about 0.5 to.
It is used in the range of 9.5 / 9.5 to 0.5. The use temperature of the oxidation catalyst does not have to be the same as the use temperature of the reduction catalyst, but in general, it is particularly necessary to select the one that can be used within the range of the use temperature of the above-mentioned reduction catalyst, which requires heating and cooling equipment. Not preferred.

[0028]

EXAMPLES Next, examples of the method of the present invention will be given, but the method of the present invention is not limited by these examples. Example 1 (Preparation of vanadium-supported sulfate group-containing titanium oxide catalyst) 1 liter of distilled water was placed in a beaker, and 200 ml of commercially available titanium tetraisopropoxide was gradually added with stirring to form a precipitate. To this, 170 ml of concentrated nitric acid was gently added with stirring to dissolve the precipitate. Then 25
200 ml of aqueous ammonia was added dropwise to adjust the pH to 8 to generate a precipitate again, and the precipitate was left standing for one day and night, filtered, washed with water and dried to obtain titanium hydroxide. 10g of this titanium hydroxide
It was taken on a filter paper, 150 ml of 0.5 mol / 1 sulfuric acid was flowed, and then air-dried. Finally, it was calcined in an air stream at 530 ° C. for 2 hours to obtain sulfate group-containing titanium oxide. Ammonium metavanadate (NH ₄ VO ₃ ) 0.23 g and oxalic acid 0.
An aqueous solution prepared by heating and dissolving 37 g of water in 2 g of water was impregnated with 5 g of the above-mentioned sulfate-containing titanium oxide, left for one day and night, and then dried in a dryer at 110 ° C. for one day and night. Finally, it was calcined in an air stream at 500 ° C. for 2 hours to obtain vanadium-supported sulfate group-containing titanium oxide. The vanadium-carrying amount of this vanadium-supported sulfate group-containing titanium oxide was 2 wt% in terms of metal with respect to the sulfate group-containing titanium oxide, and the sulfur content was 2.1 w.
It was t%.

(NOx removal reaction) 1 g of the vanadium-supported sulfate group-containing titanium oxide catalyst prepared as described above was charged into an atmospheric pressure type reaction apparatus, and 1000 ppm of nitric oxide (hereinafter referred to as "NO"). And 10% oxygen and 300
Helium gas containing ppm propane, 60 ml / min
The reaction was carried out by flowing at a flow rate of. The reaction gas was analyzed by using a gas chromatograph, and the reduction rate of NO was determined from the yield of generated nitrogen. The results are shown in Table 1 as Example 1.

Comparative Example 1 (Preparation of Titanium Oxide Catalyst) Titanium hydroxide obtained in the same manner as in Example 1 was calcined in an air stream at 500 ° C. for 2 hours to obtain titanium oxide. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that the titanium oxide prepared as described above was used as a catalyst. The results are shown in Table 1 as Comparative Example 1. As is clear from Table 1, the simple titanium oxide catalyst has almost no NO reduction activity at 300 ° C or lower.

Comparative Example 2 (Preparation of Sulfate Root-Containing Titanium Oxide Catalyst) In the same manner as in Example 1, a sulfate group-containing titanium oxide (sulfur content: 2.2 wt%) was obtained. (Removal reaction of NOx) The reduction rate of NO was examined in the same manner as in Example 1 except that the above-mentioned sulfate group-containing titanium oxide was used as a catalyst. The results are shown in Table 1 as Comparative Example 2. Table 1
As is clear from the above, the sulfate group-containing titanium oxide catalyst has much higher activity than the simple titanium oxide catalyst,
It is understood that the reducing activity at 0 ° C. or lower is smaller than that of the vanadium-supported sulfate group-containing titanium oxide catalyst of Example 1.

[0032]

[Table 1]

Example 2 (Preparation of Vanadium-Supported Titanium Oxide Catalyst Containing Sulfate Root) Commercially available titanium hydroxide containing sulfate radical (synthesized by neutralizing an aqueous titanium sulfate solution) at 500 ° C. for 2 hours in an air stream. Sintered titanium oxide containing sulfur (2.1 wt% sulfur content)
I got Ammonium metavanadate _(NH 4 _VO 3)
An aqueous solution prepared by heating and dissolving 0.23 g and 0.37 g of oxalic acid in 2 g of water was impregnated with 5 g of the above sulfate group-containing titanium oxide, and then dried under reduced pressure at 90 ° C. for 1 hour using an evaporator,
Further, it was dried in a dryer at 100 ° C. for one day. Finally, it was calcined in an air stream at 500 ° C. for 2 hours to obtain vanadium-supported sulfate group-containing titanium oxide. The vanadium supported amount of this vanadium-supported sulfate group-containing titanium oxide was 2 wt% and the sulfur content was 2.1 wt% with respect to the sulfate group-containing titanium oxide in terms of metal. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that the vanadium-supported sulfate group-containing titanium oxide prepared as described above was used as the catalyst. The results are shown in Table 2 as Example 2.

Comparative Example 3 (Preparation of sulfate group-containing titanium oxide catalyst) In the same manner as in Example 2, a sulfate group-containing titanium oxide (sulfur content 2.1 wt%) was obtained. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that the sulfate group-containing titanium oxide prepared as described above was used as a catalyst. The results are shown in Table 2 as Comparative Example 3. As is clear from Table 2, the sulfate group-containing titanium oxide catalyst which does not carry vanadium was used in Example 2
It can be seen that the activity at 300 ° C. or lower is lower than that of the vanadium-supported sulfate group-containing titanium oxide catalyst.

Example 3 NO 3 was prepared in the same manner as in Example 2 except that 500 ppm of ethyl alcohol was used as the reducing gas instead of propane.
The reduction rate of was investigated. The results are shown in Table 2 as Example 3.

[0036]

[Table 2]

Example 4 (Preparation of vanadium-supported sulfate group-containing zirconium oxide catalyst) Zirconium hydroxide was air-calcined at 400 ° C. for 2 hours to obtain amorphous zirconium oxide. Take 10 g of this zirconium oxide and add 0.50 mol / 1 sulfuric acid 100
Then, the mixture is left for 30 minutes and filtered under reduced pressure.
It was dried at ℃ for 1 day and finally, and finally calcined in an air stream at 530 ℃ for 2 hours to obtain a sulfate group-containing zirconium oxide. An aqueous solution prepared by heating 0.09 g of ammonium metavanadate (NH ₄ VO ₃ ) and 0.15 g of oxalic acid in 0.6 g of water was heated,
After impregnating 2 g of the above-mentioned zirconium sulfate oxide, it was dried under reduced pressure at 90 ° C. for 1 hour using an evaporator, and further dried in a dryer at 100 ° C. for one day. Finally, 5 in the air stream
It was calcined at 00 ° C. for 2 hours to obtain vanadium-supported sulfate group-containing zirconium oxide. The vanadium-carrying amount of this vanadium-supported sulfate-containing zirconium oxide was 2 wt% and the sulfur content was 1.3 wt% with respect to the sulfate-containing zirconium oxide in terms of metal. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that the vanadium-supported sulfate group-containing zirconium oxide prepared as described above was used as the catalyst. The results are shown in Table 3 as Example 4.

Comparative Example 4 (Preparation of Zirconium Oxide Catalyst) In the same manner as in Example 4, amorphous zirconium oxide was obtained. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that zirconium oxide prepared as described above was used as a catalyst. The results are shown in Table 3 as Example 4.
It was shown to. As is apparent from Table 3, it is understood that the simple zirconium oxide catalyst does not show NO reduction activity at 300 ° C or lower.

Comparative Example 5 (Preparation of sulfate group-containing zirconium oxide catalyst) In the same manner as in Example 4, sulfate group-containing zirconium oxide (sulfur content: 1.4
wt%) was obtained. (NOx removal reaction) The reduction rate of NO was investigated in the same manner as in Example 1 except that the sulfate group-containing zirconium oxide prepared as described above was used as a catalyst. The results are shown in Comparative Example 5
Is shown in Table 3. As is clear from Table 3, the sulfate group-containing titanium oxide catalyst has much higher activity than the simple titanium oxide catalyst, but the NO reduction activity at 300 ° C. is equal to that of the vanadium-supported sulfate group-containing zirconium oxide catalyst of Example 4. It turns out that it is small by comparison.

[0040]

[Table 3]

Example 5 (Preparation of titania-zirconia catalyst containing vanadium-supported sulfate) Titanium tetrachloride (TiCl ₄ ) was added to 1 liter of distilled water.
Dissolve 95 g and 161 g of zirconium oxychloride,
5% aqueous ammonia was gradually added to adjust the pH to 8 to form a precipitate. This was filtered, washed, and dried in a dryer at 100 ° C. 30 g of the obtained powder was put on a filter paper and
After flowing 450 ml of 5 mol / 1 sulfuric acid, it was air-dried and dried in a dryer at 100 ° C. for 1 day and then in an air stream.
Baking was performed at 30 ° C. for 2 hours to obtain sulfate group-containing titania zirconia. Ammonium metavanadate _(NH 4 _VO 3)
An aqueous solution prepared by heating 0.23 g and 0.37 g of oxalic acid into 2 g of water was impregnated in 5 g of the above-mentioned sulfate-containing titania zirconia, left for one day and night, and then dried at 110 ° C. for one day in a dryer. Finally, it was calcined in an air stream at 500 ° C. for 2 hours to obtain vanadium-supported sulfate-containing titania zirconia. The amount of vanadium supported by the vanadium-supported sulfate-containing titania zirconia was 2 wt% with respect to the sulfate-containing titania zirconia in terms of metal, and the sulfur content was 1.
It was 7 wt%. (NOx removal reaction) The reduction rate of NO was examined in the same manner as in Example 1 except that the vanadium-supported sulfate-containing titania zirconia prepared as described above was used as a catalyst. The results are shown in Table 4 as Example 5.

Comparative Example 6 (Preparation of titania-zirconia catalyst containing sulfate) Example 5
Sulfate-containing titania zirconia (sulfur content 1.8 wt%) was obtained in the same manner as in. (NOx removal reaction) Example 1 except that the sulfate group-containing titania zirconia prepared as described above was used as a catalyst.
The reduction rate of NO was examined in the same manner as in. The results are shown in Table 4 as Comparative Example 6. As is clear from Table 4, the sulfate group-containing titania zirconia catalyst which does not carry vanadium has a lower activity at 300 ° C. than the vanadium-supported sulfate group-containing titania zirconia catalyst of Example 5.

[0043]

[Table 4]

Example 6, Reference Example 1 g of the vanadium-supported sulfate group-containing titanium oxide catalyst of Example 2 as an NO reduction catalyst was placed upstream of the reactor, and commercially available 0.5% platinum alumina as an oxidation catalyst for unreacted hydrocarbons. 1 g of a catalyst was filled downstream, and a helium gas containing 1000 ppm NO, 10% oxygen and 300 ppm propane as a reaction gas was caused to flow at a flow rate of 60 ml / min to carry out the reaction. The results are shown in Table 5 as Example 6. Further, for reference, the reaction was carried out in the same manner as in Example 6 when the above oxidation catalyst was not filled. The results are also shown in Table 5. As is clear from Table 5, unreacted propane and carbon monoxide, which is an incomplete oxide, flowed out in the reference example in which the oxidation catalyst was not filled, but in Example 6 in which the oxidation catalyst was filled, It can be seen that only carbon dioxide, which is an oxide, is flowing out.

[0045]

[Table 5]

[0046]

As described above in detail, according to the method of the present invention, in an oxidizing atmosphere in which oxygen is present excessively, 300
NOx in exhaust gas efficiently even in low temperature range below ℃
Can be removed. This is because the vanadium-supported sulfate group-containing metal oxide in the method of the present invention has a high catalytic activity in a low temperature range of 300 ° C. or lower, and in the presence of hydrocarbons or oxygen-containing compounds, NOx and hydrocarbons or oxygen-containing compounds are present. This is because the reaction with the compound is preferentially promoted.

Further, the use of the oxidation catalyst may cause pollution problems such as unreacted or produced hydrocarbons, carbon monoxide, and other oxidation intermediate products which may be discharged depending on the reaction conditions. Certain substances can be fully oxidized to carbon dioxide and water vapor.

As described above, the method of the present invention is capable of efficiently removing NOx from exhaust gas from various facilities including diesel engine exhaust gas, and has an extremely high industrial value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kazuaki Kaneda, 1-1 Higashi, Tsukuba, Ibaraki Prefecture, Institute of Industrial Science and Technology (72) Inventor, Hideaki Hamada, 1-1, Higashi, Tsukuba, Ibaraki Inside the Technical Research Institute (72) Inventor Takehiko Ito 1-1, Higashi, Tsukuba-shi, Ibaraki Inside the Institute of Chemical Technology, Industrial Technology Institute (72) Inventor Moto Sasaki, 1-1, Higashi, Tsukuba-shi, Ibaraki Inside the Institute of Chemical Technology, Industrial Technology ( 72) Inventor Fujio Suganuma 228-16 Shinjuku Shinden, Showa-cho, Kita-Katsushika-gun, Saitama Prefecture (72) Inventor Mitsunori Tabata 1134-2 Gongendo, Satte City, Saitama Prefecture (72) Tadao Nakatsuji, 5-chome, Enoshima-cho, Sakai-shi, Osaka Prefecture No. 1 Sakai Chemical Industry Co., Ltd. Central Research Laboratory (72) Inventor Hiromasu Shimizu 5-1, Ebishimacho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Institute (72) Inventor Ritsu Yasukawa 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. Central Research Laboratory Yoshio Ishii (56) Reference JP-A-57-27135 Kai 54-51990 (JP, A)

Claims (2)

(57) [Claims] 1. A catalyst in which vanadium is supported on a metal oxide containing a sulfate group and an exhaust gas containing a nitrogen oxide are produced in the presence of a hydrocarbon or an oxygen-containing compound in an oxidizing atmosphere in which excess oxygen is present. A method for removing nitrogen oxides, which comprises contacting. 2. A catalyst in which vanadium is supported on a metal oxide containing a sulfate group and an exhaust gas containing a nitrogen oxide are produced in the presence of a hydrocarbon or an oxygen-containing compound in an oxidizing atmosphere containing excess oxygen. A method for removing nitrogen oxides, which comprises contacting the exhaust gas with an oxidation catalyst.