JP2506579B2 - Method for purifying exhaust gas containing nitrogen oxides - 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 for purifying a nitrogen oxide-containing exhaust gas, which comprises contacting with a specific catalyst in the presence of a compound to remove nitrogen oxide 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 in which a metal oxide such as alumina supporting a metal such as copper is brought into contact with a gas containing NOx in the presence of a hydrocarbon as a catalyst (JP-A-63-100919).

[0004]

SUMMARY OF THE INVENTION The method (a) is
Hydrocarbon components and carbon monoxide contained in automobile flue gas are made into water and carbon dioxide by a catalyst, and at the same time NOx
Is reduced to nitrogen, but combustion is performed so that the amount of oxygen contained in NOx and the amount of oxygen required to oxidize hydrocarbon components and carbon monoxide are stoichiometrically equal. In a system where excess oxygen exists, such as a diesel engine, there is a serious problem that it cannot be applied in principle.

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 a gasoline-powered vehicle, and is difficult to apply under exhaust gas conditions of a diesel engine, and the activity of the catalyst is insufficient. That is, in a catalyst in which a metal such as copper is supported on alumina or the like, not only is it poisoned by the sulfur oxides discharged from the diesel engine, but also the activity of the catalyst is reduced due to aggregation of the added metal. It is not suitable for the removal of NOx in exhaust gas from automobiles and has not been put to practical use.

The present invention has been made as a result of examining various problems existing in the above (a) to (c), and is generated from various equipment including exhaust gas of a diesel engine in an oxidizing atmosphere. It is an object of the present invention to propose a method for purifying a nitrogen oxide-containing exhaust gas capable of efficiently removing NOx in the exhaust gas.

[0008]

Means and Actions for Solving the Problems The present inventors have
As a result of repeated research to achieve the above object, it is possible to efficiently remove NOx by using a specific catalyst even in exhaust gas containing sulfur oxides without causing a decrease in activity. They have found that they can do so and have completed the present invention.

That is, the method for purifying a nitrogen oxide-containing exhaust gas of the present invention is a phyllosilicate which has been subjected to a transition metal ion exchange treatment in the presence of hydrocarbons or an oxygen-containing compound in an oxidizing atmosphere in which excess oxygen is present. It is characterized in that a catalyst containing a mineral is brought into contact with an exhaust gas containing nitrogen oxides, and the catalyst is also brought into contact with the above 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. In the method of the present invention, a phyllosilicate mineral in clay is used as a constituent of the catalyst. In general, clay is (1) adhesive, (2) an aggregate of fine particles, and (3) natural having a chemical component mainly composed of silicon, aluminum, iron, magnesium, alkali metal, and water. It is defined as a product or a compound (for example, Toshio Sudo, Clay Minerals, 1958, Iwanami Shoten, 4 pages or less).

Further, the clay minerals constituting the clay are defined in the present invention as phyllosilicate minerals of aluminum, iron, magnesium and alkali metals. Specifically, montmorillonite [general formula, X _1/3 ( Al _5/3
Mg _1/3 ) Si ₄ O ₁₀ (OH) ₂ · sH ₂ O (where X: K, Na, Ca, s: natural number, the same applies hereinafter)],
Saponite [general formula, X _1/3 (Mg ₃ ) (Al _1/3
Si _11/3 ) O ₁₀ (OH) ₂ · sH ₂ O], hectorite [general formula X _1/3 (Mg _8/3 Al _1/3 ) Si
₄ O ₁₀ (OH · F) ₂ · sH ₂ O], vermiculite [Mg ₃ (Al, Si) ₄ O ₁₀ (OH) ₂ Mg
_0.35 · 4.5H ₂ O] etc. montmorillonite group, muscovite [KAl ₂ (Si ₃ Al) (OH · F) ₂ ], biotite [KMg ₃ (Si ₃ Al) (OH · F)] etc. Mica clay mineral group, Kaolinite, Decite [All are Al
₄ (SiO ₁₀ ) (OH) ₈ ], etc. are listed (Clay Handbook, edited by The Japan Clay Society, 1).
967, Gihodo, 2 pages or less, 78 pages or less). Clay minerals (such as the clay minerals) as constituents of the catalyst in the method of the present invention
As described above , as the phyllosilicate minerals , those having an ion exchange ability are effective, and examples of those having a remarkable ion exchange ability include montmorillonite group, other mica clay mineral group and kaolinite mineral group. These Philos
In addition to natural products, there are some silicate minerals that can be synthesized such as saponite and hectorite, and the synthesis is usually performed by a hydrothermal method or a melting method. Also these phyllosilicate ores
Things, especially in natural products, not necessarily a single Firoke
Multiple phyllosilicates not necessarily composed of silicate minerals
Minerals and contaminants other than phyllosilicate minerals may be contained in some cases, and such substances can also be used as a constituent component of the catalyst in the method of the present invention.

In the above-mentioned phyllosilicate minerals , the ion exchangeable as it is as a natural product or a synthetic product is in most cases an alkali metal or alkaline earth metal ion, and in that state, the catalytic activity for the reductive decomposition of NOx is low. Low.
However, a catalyst obtained by exchanging a part or all of these ions with a transition metal ion has a high catalytic activity and is used as a catalyst in the method of the present invention.

Examples of the above-mentioned transition metals include group Ib subgroup, group II, group III, group IV, group V and group VI.
Group VII, Group VII, Group VIII metals, specifically copper, zinc, cadmium, lanthanum, zirconium,
Metals such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, palladium, and platinum, that is, transition metals in a broad sense (for example, Chemical Dictionary, Volume 5, Showa 3
6 years, Kyoritsu Publishing Co., Ltd., 437 pages or less).

In the above phyllosilicate mineral , when the exchangeable ion is a proton, the activity of so-called hydrogen clay is generally low, but a part of this proton is exchanged with the above transition metal ion. Those obtained generally show high catalytic activity and can be used as catalysts in the method of the present invention.

The transition metal ion exchange method described above is not particularly limited and can be carried out by a commonly known method. That is, a phyllosilicate mineral is immersed in an aqueous solution of a suitable transition metal salt for about several hours to about one day and night, and if necessary, heated to about 50 to 100 ° C., stirred to cause ion exchange, washed with water, dried, Further, if necessary, it is calcined to obtain the desired ion-exchanged phyllosilicate mineral . One kind of exchanged ion species may be used, or two or more kinds may be used and used.
Two or more types of phyllosilicate minerals may be used.

By the above treatment, the phyllosilicate ore
Regarding the state of the transition metal introduced into the substance , all of them may not be in the state of exchange ions. That is, the above-mentioned transition metal ion-exchanged phyllosilicate mineral is supported by the above-mentioned metal species by a method such as impregnation and deposition and, if necessary, calcined is also effective as a catalyst in the method of the present invention. The calcination treatment can be performed at any stage of catalyst preparation, and the temperature is generally about 2 though it depends on the composition of the catalyst and the like.
The temperature is from 00 to 700 ° C, preferably about 300 to 600 ° C.

Further, the above transition metal ion exchange philoke
The formate mineral may contain additives such as a carrier. As the carrier, a commonly used inorganic carrier can be applied,
Although not particularly limited, those having a large surface area are generally preferable. Specifically, inorganic oxides, that is, Al, La,
Ce, Si, Ti, Zr, Th, V, Nb, Ta, Cr
Examples thereof include oxides such as and the like, and composites of two or more of these, such as silica alumina, silica magnesia, silica titania, and alumina titania, and natural products such as pumice and diatomaceous earth can also be used. Preferred examples include alumina, silica, chromia, silica-alumina and the like. These carrier substances may be used alone or in combination of two or more. Additives such as these carriers disperse the transition metal ion-exchange clays well without inhibiting the catalytic action of the ion-exchange phyllosilicate minerals , cooperate with each other to improve the catalytic activity and selectivity, and react. It is effective in helping to remove heat and improving moldability.

Transition metal ion-exchanged phyllosilicate as a carrier
The method for supporting the mineral is not particularly limited, and the transition metal ion-exchanged phyllosilicate mineral is dispersed in water and mixed with the carrier substance, and excess water is removed by filtration, evaporation or the like and deposited on the carrier. It can be carried out by a conventionally known method such as kneading the phyllosilicate mineral with a hydrogel carrier material. When the additive such as the carrier is mixed, the compounding amount is about 9% of the catalyst composition including the additive such as the carrier.
It is 5 wt% or less, preferably about 10 to 80 wt%.

The catalyst may be used in the form of powder, granules, pellets, honeycombs, or any other shape, and its shape and structure are not particularly limited. When the catalyst is molded and used, a binder that 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.

The NOx-containing gas to be treated by the method of the present invention includes diesel engine exhaust gas such as diesel automobiles and stationary diesel engines, gasoline engine exhaust gas such as gasoline automobiles, nitric acid production facilities and various combustion facilities. Exhaust gas can be mentioned.

The removal of NOx from the exhaust gas is carried out by contacting the exhaust gas with the catalyst in the presence of the above-mentioned hydrocarbons or oxygen-containing compounds in the oxidizing atmosphere.

Here, the oxidizing atmosphere means carbon monoxide, hydrogen and hydrocarbons contained in the exhaust gas, and reducing substances of hydrocarbons or oxygen-containing compounds added as necessary in the method of the present invention. Is an atmosphere containing an excess of oxygen in excess of the amount of oxygen required to completely oxidize and convert it into water and carbon dioxide, for example, in the case of exhaust gas emitted from an internal combustion engine of an automobile, etc. The atmosphere has a large air-fuel ratio (lean region), and the excess oxygen ratio is usually about 20 to
It is about 200%.

In this oxidizing atmosphere, the above catalyst preferentially promotes the reaction between the hydrocarbons or the oxygen-containing compound and NOx over the reaction between the hydrocarbons or the oxygen-containing compound and oxygen, and NOx Is removed by reductive decomposition.

The catalyst in the method of the present invention works well in an oxidizing atmosphere, but the reducing decomposition activity against NOx decreases in a reducing atmosphere, so it is preferable to carry out the reaction in an oxidizing atmosphere.

The reducing substances for reducing and decomposing hydrocarbons or oxygen-containing compounds, that is, NOx, to be present may be hydrocarbons remaining in the exhaust gas or particulates which are incomplete combustion products such as fuels. When the amount is insufficient to accelerate the above 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 when the required NOx removal rate is low, for example, it may be smaller than the theoretical amount required for reductive decomposition of 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 oxygenates is about 20 to 2,000% excess, preferably about 30 to 1.5, of the theoretical amount required for the reductive decomposition of NOx.
It is present in a 00% excess.

Here, the necessary theoretical amount of hydrocarbons and oxygen-containing compounds means that oxygen is present in the reaction system. Therefore, in the method of the present invention, it is necessary to reductively decompose nitrogen dioxide (NO ₂ ). Is defined as a hydrocarbon or an oxygen-containing compound. For example, when propane is used as a hydrocarbon, 1,000 ppm of nitric oxide (NO) is reduced and decomposed in the presence of oxygen. It becomes 200 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.

By the above catalyst in the method of the present invention, N
As a reducing substance for reducing Ox, any substance is effective as long as it is a carbon-containing substance such as a flammable organic compound. However, from the viewpoint of practicality, compounds such as nitrogen, sulfur, and halogen are expensive, secondary, and so on. There are many problems such as the generation of dangerous harmful substances and damage to the catalyst, and solid substances such as carbon black and coal are generally not preferable in terms of supply to the catalyst layer, contact with the catalyst, etc. Oxygen compounds are preferred.

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 methane,
When hydrocarbon gases such as ethane, ethylene, propane, propylene, butane, and butylene are in liquid form, liquid hydrocarbons include single hydrocarbons such as pentane, hexane, octane, heptane, octene, benzene, toluene, xylene, gasoline, and kerosene. And mineral oil-based hydrocarbon oils such as light oil and heavy oil. Further, the oxygen-containing compound in the method of the present invention means an oxygen-containing organic compound, and alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol and octyl alcohol, ethers such as dimethyl ether, ethyl ether and propyl ether, methyl acetate, Oxygen-containing organic compounds such as esters such as ethyl acetate and oils and fats, ketones such as acetone and methylethylketone are exemplified, and these hydrocarbons or oxygen-containing compounds may be used alone. More than one species may be used.

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

The reaction is carried out by preparing a reactor in which the above catalyst is arranged, allowing a hydrocarbon or an oxygen-containing compound to exist in an oxidizing atmosphere, and passing an 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 thus is not particularly limited.
r ^-1 , preferably in the range of about 1,000 to 70,000 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.

The oxidation catalyst which can be used in the method of the present invention may be any one as long as it can completely combust the above incomplete combustion products, but it may be activated alumina, silica, zirconia or the like. 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, in particular, base metal oxides and the like can be used without being supported on a carrier.

The additives added for the purpose of the shape of the oxidation catalyst, molding, etc. are the same as those in the case of the reduction catalyst, and various kinds 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)
There is a method of disposing 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 9.5.
/9.5 to 0.5.

The use temperature of the oxidation catalyst may not be the same as the use temperature of the reduction catalyst, but generally, the heating / cooling equipment should be selected within the range of the use temperature of the above-mentioned reduction catalyst. It is preferable because it is not necessary.

[0039]

EXAMPLES Next, examples of the method of the present invention will be described, but the method of the present invention is not limited to these examples. Example 1 (Preparation of hectorite) Preparation of solution A: 129 g of water glass (JIS No. 3) was added to water 45
It was dissolved in 0 ml. While vigorously stirring the solution, 45 ml of concentrated hydrochloric acid was added dropwise at once to prepare a uniform and transparent silica sol (solution A). Preparation of solution B: 82.5 g of magnesium chloride (hexahydrate) was dissolved in 150 ml of water (solution B). Solution A was slowly added dropwise while stirring solution A. This was further stirred to form a slurry, and 300 ml of concentrated aqueous ammonia was slowly added dropwise. The generated gel was thoroughly washed with water to remove excess salts. To this, 4.2 g of lithium hydroxide (monohydrate)
Was dissolved in 45 ml of water, stirred well to form a slurry, charged into an autoclave, and reacted with stirring at 200 ° C. for 6 hours. The produced hectorite aqueous solution was evaporated into water under reduced pressure using a rotary evaporator and then dried to obtain powdered hectorite.

(Preparation of Cu-exchanged hectorite) 30 g of the above hectorite powder was added to 1 liter of water, and the mixture was heated to 60 ° C.
On a hot water bath, the mixture was heated and stirred to be dissolved to obtain a sol liquid. While stirring, 0.5N copper ammonia complex salt (hydrochloride)
200 ml was dropped slowly. The product in the form of a slurry was allowed to stand for a whole day and night, the produced Cu exchanger was aggregated and settled, then washed sufficiently with water until copper ions were not detected in the filtrate, and dried to obtain Cu-exchanged hectorite.

(NOx removal reaction) 1 g of the Cu-exchanged hectorite prepared as described above was charged into a normal pressure flow reactor, and 1000 ppm of nitric oxide (hereinafter referred to as "N
O "), 10% oxygen, and helium gas containing 300 ppm propylene were flowed at a flow rate of 60 ml / min to carry out the reaction. The analysis of the reaction gas was carried out using a gas chromatograph, and the reduction decomposition of NO was carried out. The rate was determined from the yield of nitrogen produced, and these results are shown in Table 1.

Example 2 (Preparation of Cu-exchanged montmorillonite) Commercially available montmorillonite (Kunipia F, manufactured by Kunimine Industries Co., Ltd.)
25 g was mixed and dispersed in 800 ml of a 0.25N copper nitrate aqueous solution, left overnight with occasional shaking, filtered, and washed sufficiently with water until copper ions were not detected in the filtrate. After performing this operation twice, it was dried to obtain Cu-exchanged montmorillonite.

(NOx removal reaction) Using the above-mentioned Cu-exchanged montmorillonite as a catalyst, NO was removed in the same manner as in Example 1.
Was examined for reductive decomposition rate. The results are also shown in Table 1.

Example 3 (Preparation of Cu-exchanged saponite) In the preparation of Cu-exchanged montmorillonite of Example 2, Example 2 was repeated except that 20 g of commercially available saponite was used instead of montmorillonite.
A Cu-exchanged saponite was prepared in the same manner as in.

(NOx removal reaction) The reduction decomposition rate of NO was examined in the same manner as in Example 1 using the Cu-exchanged saponite as a catalyst. The results are also shown in Table 1.

Example 4 (Preparation of Ni-exchanged saponite) In the same manner as in Example 3 except that a 0.5N nickel nitrate aqueous solution was used in place of the copper ammonia complex salt aqueous solution in the preparation of the Cu-exchanged saponite of Example 3. A Ni-exchanged saponite was prepared.

(NOx removal reaction) In the NO removal reaction of Example 1, using the above Ni-exchanged saponite as a catalyst, 1000 ppm of NO and 1000 pp of propylene were used.
m, except that helium gas containing 10% oxygen was used,
The reduction decomposition rate of NO was examined in the same manner as in Example 1. The results are also shown in Table 1.

Example 5 (Preparation of Fe-exchanged saponite) In the preparation of Cu-exchanged saponite of Example 3, a 0.5N iron (III) nitrate aqueous solution was used in place of the copper ammonia complex salt aqueous solution.
An Fe-exchanged saponite was prepared in the same manner as in Example 3.

(NOx removal reaction) The reduction decomposition rate of NO was examined in the same manner as in Example 4 using the Fe-exchanged saponite as a catalyst. The results are also shown in Table 1.

Example 6 (Preparation of Mn-exchanged saponite) As in Example 3 except that a 0.5N manganese (II) nitrate aqueous solution was used in place of the copper ammonia complex salt aqueous solution in the preparation of the Cu-exchanged saponite of Example 3. Similarly, Mn-exchanged saponite was prepared.

(NOx removal reaction) The reduction decomposition rate of NO was examined in the same manner as in Example 4 using the Mn-exchanged saponite as a catalyst. The results are also shown in Table 1.

Example 7 In the NOx removal reaction of Example 1, the charged amount of Cu-exchanged hectorite catalyst was 0.1 g, and NO was 1000 pp.
m, methyl alcohol weight conversion of propylene 800p
The reduction decomposition rate of NO was examined in the same manner as in Example 1 except that a helium gas containing pm and 10% oxygen was used. The results are also shown in Table 1.

Comparative Example 1 (Preparation of H-type montmorillonite) 10 g of montmorillonite of Example 2 was dissolved in 500 ml of water to obtain a sol-like liquid. To this, 30 ml of H-type strongly acidic cation exchange resin (wet state) was added, and occasionally stirred and kept for about 3 hours to exchange ion-exchangeable metal ions (mainly sodium) in montmorillonite with protons, and filter to obtain a sol. The liquid and the resin were separated. After repeating the above operation three times, the sol-like liquid was evaporated under reduced pressure by a rotary evaporator and further dried to obtain powdery H-type montmorillonite (so-called hydrogen clay or clay acid).

(NOx removal reaction) Using the above H-type montmorillonite as a catalyst, the reduction decomposition rate of NO was examined in the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 2 Using the commercially available montmorillonite (Kunipia F) used in the preparation of the Cu-exchanged montmorillonite of Example 2 as it was as a catalyst, the reduction decomposition rate of NO was examined in the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 3 The commercially available saponite used in the preparation of the Cu-exchanged saponite of Example 3 was used as it was as a catalyst, and Example 1 was used.
The reduction decomposition rate of NO was examined in the same manner as in. The results are also shown in Table 1.

Examples 8 to 9, Reference Example 1 g of the Cu-exchanged hectorite of Example 1 as a NOx reduction catalyst was placed upstream in the reaction vessel, and a commercially available 0.5% palladium-supported alumina was used as an oxidation catalyst for unreacted hydrocarbons. Catalyst 1
Then, g was charged downstream, and the reduction decomposition rate of NO was examined in the same manner as in Example 1 (Example 8). Table 2 shows the results.

Further, the reductive decomposition rate of NO was examined in the same manner as above using 1 g of a catalyst in which 30% ferric oxide was supported on alumina as an oxidation catalyst (Example 9). The results are also shown in Table 2. The oxidation catalyst of Example 9 in which ferric oxide was supported on alumina was prepared by dissolving 38 g of ferric nitrate (Fe (NO ₃ ) ₃ .9H ₂ O) in 300 ml of distilled water and adding it to a commercially available solution. 35 g of γ-alumina was added with stirring, and 14% ammonia water was added dropwise until pH 8 to deposit iron hydroxide on the alumina, followed by filtration, washing with water, drying, and then calcination in air at 500 ° C. for 3 hours. Obtained.

Further, as a reference, the reduction decomposition rate of NO was examined in the same manner as in Examples 8 and 9 when the oxidation catalysts of Examples 8 and 9 were not filled (Reference Example). The results are also shown in Table 2.

As is clear from Table 2, in the reference example in which the oxidation catalyst is not filled, unreacted propylene and carbon monoxide which is an incomplete oxide flow out. In Nos. 8 and 9, it can be seen that only carbon dioxide, which is a complete oxide, is flowing out.

[0061]

[Table 1]

[0062]

[Table 2]

As is clear from the above tables, in the method of the present invention, reductive decomposition of NOx occurs efficiently even in the presence of excess oxygen, and it is effective for actual exhaust gas containing sulfur oxides. I know there is.

[0064]

As described above in detail, according to the method of the present invention, NOx in exhaust gas can be efficiently removed in an oxidizing atmosphere in which oxygen is excessively present. this is,
Phyllo treated by transition metal ion exchange in the method of the present invention
This is because the silicate mineral preferentially promotes the reaction between NOx and the hydrocarbons or oxygen-containing compounds in the presence of the hydrocarbons or oxygen-containing compounds.

Furthermore, the use of an 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 completely 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 (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 53/36 102C (74) Above two agents Attorney Chiga Kubota (1 person outside) (72) ) Inventor Fujio Suganuma 228-16 Shinjuku, Shinjuku, Showa-cho, Kita-Katsushika-gun Saitama (72) Inventor Akihiro Kitazume 2-15-36 Sugito, Sugito-cho, Kita-Katsushika-gun Saitama (72) Inventor Mitsunori Tabata 1134 Gongendo, Satte-shi, Saitama -72 (72) Inventor Tadao Nakatsuji, 5-1, Ebishima-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. (72) Inventor, Hiromasu Shimizu 5--1, Ebisu-cho, Sakai City, Osaka Prefecture Sakai Chemical Industry Co., Ltd. In-house (72) Inventor, Yoshiaki Kaneda, 1-1, Higashi, Tsukuba-shi, Ibaraki Institute of Industrial Science and Technology (72) Inventor, Motoki Sasaki, 1-1, Higashi, Tsukuba, Ibaraki Industrial Technology Institute Institute of Technology in the examiner Yoshio Ishii (56) Reference Patent flat 4-77310 (JP, A)

Claims (2)

(57) [Claims] 1. A catalyst comprising a phyllosilicate mineral that has undergone a transition metal ion exchange treatment in the presence of hydrocarbons or an oxygen-containing compound in an oxidizing atmosphere in which excess oxygen is present, and an exhaust gas containing nitrogen oxides. A method for purifying a nitrogen oxide-containing exhaust gas, comprising: 2. A catalyst composed of a transition metal ion-exchanged phyllosilicate mineral and an exhaust gas containing nitrogen oxides are contacted with each other in the presence of hydrocarbons or an oxygen-containing compound in an oxidizing atmosphere containing excess oxygen. And then contacting the exhaust gas with an oxidation catalyst.