JP2847021B2 - Method for reducing and removing nitrogen oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a process for producing nitrogen oxides in an exhaust gas, which contains a small amount of added hydrocarbons or oxygen-containing organic compounds, or remains in the exhaust gas under oxidizing conditions in which excess oxygen is present. The present invention relates to a method for removing nitrogen oxides in exhaust gas by contacting a specific alumina catalyst in the presence of a hydrocarbon or an oxygen-containing organic compound.

[0002]

2. Description of the Related Art Nitrogen oxides in various exhaust gases (hereinafter referred to as "nitrogen oxides").
Since “NOx” is harmful to health and can cause photochemical smog and acid rain, development of an effective treatment means is desired.

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 catalyst method for gasoline vehicles, and (b) a selective catalytic reduction method using ammonia for exhaust gas from large equipment discharge sources such as boilers. Other proposed methods include (c) N2 in exhaust gas using hydrocarbons.
As a method for removing Ox, a method is used in which a metal oxide such as alumina carrying a metal such as copper is brought into contact with a gas containing NOx in the presence of a hydrocarbon as a catalyst (Japanese Patent Laid-Open No. 63-10 / 1988).
No. 0919).

[0004]

SUMMARY OF THE INVENTION The method (a) is
Hydrocarbon components and carbon monoxide contained in automobile exhaust gas are converted into water and carbon dioxide by a catalyst, and simultaneously NOx
Is reduced to nitrogen, but combustion is performed so that the amount of oxygen contained in the exhaust gas and the amount of oxygen required to oxidize hydrocarbon components and carbon monoxide are chemically equivalent. In a system in which 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 treated as a high-pressure gas in many cases. Therefore, the handling is not easy, the equipment becomes large, and a small exhaust gas is generated. Application to sources, especially mobile sources, is technically extremely difficult and economical.

[0006] On the other hand, the method (c) is mainly intended for gasoline-powered vehicles, and is difficult to apply under exhaust gas conditions of a diesel engine and has insufficient catalyst activity. In other words, since a metal such as copper is contained as a component of the catalyst, not only is it poisoned by sulfur oxides discharged from the diesel engine, but also the activity of the catalyst decreases due to aggregation of the added metal and the like. It is not suitable for removing NOx in exhaust gas from wastewater, and has not been put to practical use.

The present invention has been made as a result of examining the various problems existing in the above (a) to (c), and is produced from various facilities including exhaust gas of a diesel engine even in an oxidizing atmosphere. It is an object of the present invention to propose a method for efficiently removing NOx in an exhaust gas containing sulfur oxides.

[0008]

Means and Action for Solving the Problems The present inventors have
In order to achieve the above object, as a result of repeated studies, the use of a specific alumina catalyst has enabled a higher NOx concentration in exhaust gas containing sulfur oxides than in the past.
Have been found, and the present invention has been completed.

That is, the method for removing NOx according to the present invention is characterized in that (1) one or both of an alkali metal and an alkaline earth metal in an oxidizing atmosphere containing excess oxygen in the presence of hydrocarbons or oxygen-containing organic compounds. (2) a pore volume formed from pores having a diameter of 60 ° or less is 0.06 cm ³ / g or more;
And the volume of pores formed from pores having a diameter of 80 ° or less is 0.
The method is characterized in that an alumina catalyst of 1 cm ³ / g or more is brought into contact with an exhaust gas containing nitrogen oxides.

The details of the present invention will be described below together with the operation. The catalyst which can be used in the present invention is the above (1)
The reason why these requirements are required for the alumina catalyst satisfying the requirements of (2) and (2) will be described below for each requirement.

Regarding the requirement of (1); the basic reaction of the present invention is that propane (C ₃ H ₈ ) is used as a hydrocarbon or an oxygen-containing organic compound, and nitrogen dioxide (NO) is used as NOx.
_{If 2} ) is taken as an example, it is presumed to be based on the reaction formula shown in Chemical formula 1.

[0012]

Embedded image

That is, in order to reduce NO ₂ to N ₂ , it is necessary to oxidize C ₃ H ₈ to CO ₂ and H ₂ O. If the oxidation of C ₃ H ₈ does not proceed, NO The reduction of ₂ does not progress either. However, if the oxidation of C ₃ H ₈ progresses too much, C ₃ H ₈ does not participate in the reaction of the chemical formula 1, and as a result, the reduction rate of NO ₂ also decreases. Therefore, NOx
To reduce NO at a high rate, C ₃ which is a NOx reducing agent is used.
Hydrocarbons or oxygen-containing organic compounds such as H ₈ (hereinafter, hydrocarbons or oxygen-containing organic compound "reducing agent"
(Sometimes referred to as). In order to promote appropriate oxidation of such a reducing agent, an alumina catalyst is used in the present invention.

By the way, when an alumina catalyst is used,
Even if the degree of oxidation of the reducing agent is the same, the NOx reduction and removal efficiency (meaning the NOx removal rate converted per reducing agent consumed by oxidation) may be significantly different. As a result of studying the cause, it has been found that the NOx reduction removal efficiency is related to impurities in the alumina catalyst, and particularly that an alkali metal or an alkaline earth metal greatly affects the NOx reduction removal efficiency. Therefore, in the present invention, the content of one or both of the alkali metal and the alkaline earth metal of the alumina catalyst is set to a certain amount or less, specifically, about 0.5 wt% or less, preferably about 0.1 wt% or less. It is.

The content of one or both of the alkali metal and the alkaline earth metal is preferably as small as possible, and the lower limit is not particularly limited. It can be almost zero due to the progress of the technology for measuring the content of.

Further, it is preferable that the content of sulfur is as small as possible together with these alkali metals and alkaline earth metals in order to enhance the NOx reduction and removal efficiency.
More specifically, the sulfur content is preferably about 0.1 wt% or less as in the case of alkali metals and alkaline earth metals.

In the present invention, the content of one or both of the alkali metal and the alkaline earth metal is about 0.5.
The catalyst uses an alumina catalyst of not more than wt%. Of course, as described above, when the content of one or both of the alkali metal and the alkaline earth metal is substantially 0, and when the content of sulfur is also substantially 0, Al excluding moisture is removed.
The composition ratio as ₂ O ₃ may be about 100 wt%.

Regarding the requirement (2): In order to promote the appropriate oxidation of the reducing agent as described above to increase the NOx reduction removal efficiency at a lower temperature and at a higher speed (high SV), the present inventors have proposed a method. As disclosed in Japanese Patent Application No. 4-231376 (hereinafter referred to as "prior proposal"), the size of the pore volume formed by pores having a specific diameter or less is an important factor. . The larger the pore volume, the better the appropriate oxidation of the reducing agent can proceed.

In the prior proposal, the specific diameter is 80
The diameter of Å or less is important, indicating that the pore volume formed by these pores greatly affects the oxidation rate of the reducing agent. However, as a result of a detailed study, a smaller diameter occupying a pore volume of 80 ° or less,
Specifically, it was confirmed that the pore volume formed by pores having a diameter of about 60 ° or less also contributed to the oxidation rate.

[0020] That is, the pore volume formed by pores with a size of less than or equal to about 60Å is, 0.06 cm ³ / g or more, preferably 0.08 cm ³ / g or more, more preferably 0.10 cm ³ or more And a pore volume formed by pores having a diameter of about 80 ° or less is 0.1 cm ³ /
When the amount is not less than g, preferably not less than 0.15 cm ³ / g, more preferably not less than 0.2 cm ³ / g, appropriate oxidation of the reducing agent can be favorably advanced.

In this case, the volume of pores having a diameter of 80 ° or less is 0.1 mm.
The pore volume of a diameter of 60 ° or less is not particularly limited as long as it has a diameter of 26 cm ³ / g or more (see the previous proposal),
When the pore volume at 0 ° or less is less than 0.26 cm ³ / g, the size of the pore volume at 60 ° or less greatly affects the reaction characteristics, particularly the oxidation characteristics of the reducing agent.

The upper limit of the volume of pores having a diameter of 60 ° or less is as follows:
Although not particularly limited, an excessively large one lacks practicality because the manufacturing technique becomes difficult, and even if it can be manufactured, the cost rises. In addition, when the number of small pores having a diameter of 60 ° or less is increased, sintering that causes a change in the properties of the catalyst carrier is likely to occur, and the surface area is reduced. In the alumina catalyst of the present invention, it is needless to say that the larger the surface area, the better. Therefore, the upper limit of the pore volume formed by pores having a diameter of 60 ° or less is not particularly limited, but is about 0.2 cm ³ / g. It is preferable that
For the same reason, the upper limit of the pore volume formed by pores having a diameter of 80 ° or less is also about 0.6 cm ³ / g, preferably about 0.4 cm ³ / g, more preferably about 0.26 cm ³ / g.
Suitable around cm ³ / g.

The reason why the pore size of the alumina catalyst in the present invention controls the reaction characteristics has not been elucidated yet, but the following reasons are presumed.

Generally, the inner surface of a porous solid catalyst is significantly larger than the outer surface, and the catalytic reaction proceeds substantially on the inner surface. At this time, the reactive molecules diffuse from the outer surface into the pores and move to the inner surface where active points are distributed.
In a relatively large pore that cannot be forcedly flowed, the reaction molecules undergo normal molecular diffusion in which they move while repeating collision with each other. On the other hand, in a sufficiently small micropore region, the reactive molecules move mainly by Knudsen diffusion due to collision with the tube wall.

On the specific alumina catalyst having a large number of pores having a diameter of 60 ° or 80 ° in the present invention, a relatively large number of reactive molecules move by Knudsen diffusion, so that more reactive molecules are located at the catalytically active sites. It is considered that contact is possible, and the reaction is further promoted.

In order to determine the pore volume of the requirement (2) which has such an effect, first, as described in the previous proposal, first,
While the surface area is determined from the nitrogen adsorption isotherm by the BET method, the pore distribution is measured by a nitrogen adsorption and desorption isotherm (-196 ° C) up to a relative pressure of 0.967, and then measured by the BJH method or the DH method. The distribution for pores with a radius of 200 ° or less is determined. Next, the pore volume of the requirement (2) is calculated from these results. The physical properties of the alumina catalyst according to the present invention are as follows.
This is measured for alumina that has been used for more than an hour.

The alumina catalyst of the present invention satisfying the requirements (1) and (2) can be produced by various known methods. To briefly explain an example, first, an aluminum hydrate is prepared from aqueous solutions of various aluminum salts as raw materials, and then this is calcined (pyrolyzed) to obtain alumina. By the way, when preparing aluminum hydrate, various alumina hydrates are produced by adjusting conditions such as the concentration or pH of the raw material aqueous solution, the aging time, and the temperature at the time of precipitation. For example, when preparing a precipitate of alumina hydrate from an aqueous solution of sodium aluminate and carbon dioxide, boehmite (pseudo-boehmite), bayerite, gypside, and the like are generated by adjusting the above various conditions. Of these hydrates, alumina obtained by calcining low crystallinity such as pseudo-boehmite is used to calcine aluminum hydrate containing a large amount of high crystallinity such as bayerite and gypside. The specific surface area and the pore volume are larger than the alumina obtained by the above method, which is preferable.

Next, a method for controlling the pore structure of the alumina catalyst of the present invention so as to satisfy the above requirement (2) will be described by taking, as an example, a case where the above-described pseudo-boehmite (boehmite gel) is obtained by calcination. Will be explained. When the boehmite gel is observed with an electron microscope, a fibrous or thin plate-like aggregate is observed. Then, between the structure of the boehmite gel and the pores of alumina, if schematically represented, those composed of small basic particles give small pores by baking, and large ones form large pores. It can be seen that a uniform pore size gives a sharp pore distribution, and a non-uniform particle gives a broad pore distribution. Therefore, by controlling the basic particles of the boehmite gel, the pore structure can be controlled.

A specific example is described in JP-A-58-21.
3832, 58-190823, USP 4,
As disclosed in 562,059 and 4,555,394, etc., by controlling the pH of a solution in which boehmite gel is present, fine crystals present in the solution are dissolved and erased. And the operation of growing small crystals without growing large crystals, the particle size can be made uniform. The particle size at this time can be controlled by adjusting pH, aging time, and the like. Also, when obtaining an alumina fired body from a hydrate, by adjusting the firing temperature, an alumina fired body having a different pore volume and a different pore distribution can be obtained.

As a method for controlling the pore volume, a method in which a water-soluble polymer compound such as polyethylene glycol is added to the boehmite gel (Japanese Patent Laid-Open No. 52-104498).
And JP-A-52-77891), and a method of substituting a part or most of water in a boehmite sol with an oxygen-containing organic compound such as alcohol (JP-A-50-123588). However, many of these conventional methods are not suitable for controlling micropores (20 ° or less) important in the present invention or controlling the pores in the first half of mesopores (20 to 500 °).

The above catalyst can be used in the form of powder, granules, pellets, honeycombs, etc.
The structure does not matter. When the catalyst is used after being molded, a binder usually used at the time of molding, such as polyvinyl alcohol, and a lubricant, that is, graphite, wax, fatty acids, carbon wax, and the like can also be used.

The NOx-containing gas to be treated in the present invention includes exhaust gas from diesel engines such as diesel vehicles and stationary diesel engines, gasoline engines such as gasoline vehicles, nitric acid production facilities, and various combustion facilities. Can be mentioned. The removal of NOx from these exhaust gases is carried out by using the above-mentioned catalyst and bringing the exhaust gas into contact with the catalyst in an oxidizing atmosphere containing excess oxygen in the presence of hydrocarbons or oxygen-containing organic compounds.

Here, the oxidizing atmosphere refers to the carbon monoxide, hydrogen, hydrocarbons or oxygen-containing organic compound contained in the exhaust gas, and the hydrocarbons or oxygen-containing organic compound added as necessary in the present invention. Refers to an atmosphere containing oxygen in excess of the amount of oxygen necessary to completely oxidize the reducing agent to water and carbon dioxide. For example, in the case of exhaust gas discharged from an internal combustion engine such as an automobile, the atmosphere is in a state where the air ratio is large (lean range), and the excess oxygen rate is usually about 20 to 200%. In this oxidizing atmosphere, the catalyst preferentially prefers the reaction of hydrocarbons or oxygen-containing organic compounds with NOx as shown in Chemical Formula 1 over the reaction of hydrocarbons or oxygen-containing organic compounds with oxygen. Promote NOx removal.

As the reducing agent for reducing and removing hydrocarbons or oxygen-containing organic compounds to be present, that is, NOx, there is used a patty which is an incomplete combustion product such as hydrocarbons or oxygen-containing organic compounds or fuel remaining in the exhaust gas. Curing may be used, but when the amount is less than that required for promoting the reaction as shown in Chemical formula 1, it is necessary to add hydrocarbons or oxygen-containing organic compounds from the outside.

The amount of the hydrocarbons or the oxygen-containing organic compound is not particularly limited. For example, when the required NOx removal rate is low, the amount may be smaller than the theoretical amount required for the reductive decomposition of NOx. However, it is generally preferred to use an excess in excess of the necessary stoichiometric amount, since the reduction reaction proceeds more. Usually, it is preferably present in excess, and usually about 20 to 2,000% of the theoretical amount required for reductive decomposition of NOx, Preferably about 30 to
1,500% excess.

Here, the stoichiometric amount of the necessary hydrocarbons or oxygen-containing organic compounds means that there is oxygen in the reaction system. Therefore, in the present invention, the necessary stoichiometric amount is required for reductive decomposition of nitrogen dioxide (NO ₂ ). Is defined as a natural hydrocarbon or an oxygen-containing organic compound. For example, the theoretical amount of propane when reductively decomposing 1,000 ppm of nitrogen monoxide (NO) in the presence of oxygen using propane as a hydrocarbon Is 20
It becomes 0 ppm. Generally, depending on the amount of NOx in the exhaust gas, the amount of hydrocarbons or oxygen-containing organic compound to be present is about 50 to 10,000 ppm in terms of methane.

Specific examples of the hydrocarbons in the present invention include gaseous hydrocarbon gases such as methane, ethane, ethylene, propane, propylene, butane and butylene, and liquid hydrocarbons such as pentane. , Hexane, octane, heptene, benzene, toluene, xylene and the like; and mineral oils such as gasoline, kerosene, light oil and heavy oil. Specific examples of the oxygen-containing organic compound in the present invention include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and octyl alcohol, dimethyl ether, ethyl ether, ethers such as propyl ether, methyl acetate, ethyl acetate, and fats and oils. And ketones such as acetone and methyl ethyl ketone. These hydrocarbons or oxygen-containing organic compounds may be used alone or in combination of two or more.

Incidentally, unburned or incompletely burned products such as fuels present in the exhaust gas, that is, hydrocarbons, oxygen-containing organic compounds, and particulates are also effective as reducing agents. Alternatively, it is contained in oxygen-containing organic compounds. This means that the above-mentioned specific alumina catalyst of the present invention also has a function as a catalyst for reducing and removing hydrocarbons, oxygen-containing organic compounds and particulates in exhaust gas.

The NOx removal reaction in the present invention is carried out by preparing a reactor in which the above-mentioned specific alumina catalyst is disposed, and passing a NOx-containing exhaust gas in the presence of a hydrocarbon or an oxygen-containing organic compound. The reaction temperature at this time, the optimum reaction temperature is slightly different depending on the type of alumina catalyst or the type of hydrocarbons or oxygen-containing organic compounds, but a temperature close to the temperature of the exhaust gas is preferable because heating equipment for the exhaust gas becomes unnecessary, and is generally preferable. About 200-800 ° C,
Preferably it is about 300-600 ° C. The reaction pressure is not particularly limited, and the reaction proceeds under increased pressure or reduced pressure,
It is convenient to introduce the exhaust gas into the catalyst layer at normal exhaust pressure to allow the reaction to proceed. The space velocity (SV) is determined by the type of alumina catalyst, other reaction conditions, the required NOx removal rate, and the like, and thus is not particularly limited, but is generally about 500 to 500.
100,000 hr ^-1 , preferably about 1,000 to 7
It is in the range of 0.001 hr- ¹ . In the present invention, when treating the exhaust gas from the internal combustion engine, it is preferable to arrange the exhaust gas downstream of the exhaust manifold.

When the exhaust gas is treated by the above-described method of the present invention, depending on the treatment conditions, unburned hydrocarbons or oxygen-containing organic compounds, or imperfections such as carbon monoxide which cause pollution. Combustion products may be emitted into the process gas. This problem can be solved by contacting a gas treated with the above-mentioned specific alumina catalyst of the present invention (hereinafter sometimes referred to as “reduction catalyst”) with an oxidation catalyst in an oxidizing atmosphere. it can.

The oxidation catalyst that can be used in the present invention may be any one that can completely combust the above-mentioned incomplete combustion products. Platinum, activated alumina, silica, zirconia, etc. Catalyst components such as precious metals such as palladium and ruthenium, base metal oxides such as lanthanum, cerium, copper, iron, and molybdenum, and perovskite-type crystal structures such as cobalt lanthanum trioxide, iron lanthanum trioxide, and cobalt strontium trioxide are used alone. Or those carried in combination. In this case, the supported amount of the catalyst component is about 0.
It is about 01 to 2 wt%, and about 5 to 70 wt% for base metal oxides and the like. Of course, in particular, base metal oxides and the like can be used without being supported on a carrier. Additives added for the purpose of shape, molding, etc. of the oxidation catalyst are the same as those in the case of the reduction catalyst, and various additives 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 according to the required performance. Particularly, when the substance to be oxidized and removed is a hydrocarbon such as carbon monoxide or an intermediate oxide of an oxygen-containing organic compound. Although it is possible to use a mixture of a reduction catalyst and an oxidation 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.

As a specific example of purifying exhaust gas by using these catalysts, a reactor in which a reduction catalyst is disposed is disposed in an exhaust gas introduction section (front stage), and a reactor in which an oxidation catalyst is disposed is disposed in an exhaust gas discharge section (rear stage). There is a way to use it. Further, the respective catalysts can be arranged and used 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 used in the range of about 0.5 to 9.5 / 9.5 to 0.5, expressed as (A) / (B).
The temperature at which the oxidation catalyst is used may not be the same as the temperature at which the reduction catalyst is used, but in general, it is particularly necessary to select heating and cooling equipment that can be used within the range of the temperature at which the reduction catalyst is used. Preferred.

[0044]

【Example】

Example 1 1 g of an alumina catalyst (trade name “N611” manufactured by JGC Chemicals Co., Ltd.) having the characteristics shown in Table 1 was charged into a normal-pressure flow reactor, and 1000 ppm of nitrogen monoxide, 10% oxygen, and 1000 ppm were added thereto. Of methanol and helium gas containing 8% water vapor were passed under a contact time of 0.2 g · s · cm ^{−3 to} carry out the reaction. Analysis of the reaction gases, by gas _{chromatography,} N _2, N 2 O, CO, quantified and CO _2, NO reduction removal rate than yield _{N 2} (NO in _{N 2}
Conversion). The results are shown in Table 1 in Example 1.
As shown.

[0045]

[Table 1]

From Table 1, it can be seen that the content of the alkali metal and alkaline earth metal is very small, the pore volume with a diameter of 60 ° or less is 0.06 cm ³ / g or more, and the pore volume with a diameter of 80 ° or less is 0.1 mm. When the alumina catalyst of the present invention of 1 cm ³ / g or more is used, it can be seen that NOx can be reduced and removed with very high efficiency even in an atmosphere where steam is present.

Comparative Examples 1 to 5 (Preparation of alumina catalyst containing alkali metal and alkaline earth metal) 0.93 g of sodium nitrate, 0.6 of potassium nitrate
6 g, calcium nitrate tetrahydrate 1.5 g, magnesium nitrate hexahydrate 2.7 g, and barium nitrate 0.49 g were dissolved in ion-exchanged water 35 g to prepare aqueous solutions, respectively, and alumina (a product of Nikki Chemical Co., Ltd.) Name "N611") 50
g was impregnated and supported. These were dried at 100 ° C. for 24 hours, and then calcined at 600 ° C. in an air stream for 3 hours. The weight% of the alkali metal and alkaline earth metal in the obtained alumina catalyst is assuming that alumina is 100%.
Na: 0.51 wt%, K: 0.55 wt, respectively
%, Ca: 0.52 wt%, Mg: 0.56 wt%, B
a: 0.52% by weight.

(NO Reduction Reaction) The NO reduction removal rate was examined in the same manner as in Example 1 using the alkali metal and the alkali metal-containing alumina catalyst prepared as described above.
The results are shown in Tables 2 and 3 as Comparative Examples 1 to 5.

[0049]

[Table 2]

[0050]

[Table 3]

According to Tables 2 and 3, the alumina catalyst containing 0.5% by weight or more of alkali metal or alkaline earth metal is:
Significant NO compared to the alumina catalyst shown in Example 1 which contains almost no alkali metal or alkaline earth metal
It can be seen that the reduction and removal efficiency decreases. In particular, N
Alumina catalysts containing alkali metals such as a and K have a large degree of activity reduction.

Examples 2 to 4 (Preparation of alumina catalysts having different physical properties) Concentration 1344
g / liter (hereinafter, referred to as “L” and milliliter is referred to as “mL”) by diluting 25 mL of an aqueous solution of aluminum sulfate with 3000 mL of ion-exchanged water;
After mixing with 175 mL of 97 g / L aqueous sodium aluminate solution, the mixture was heated to 90 ° C. with stirring. A 134 g / L aqueous solution of aluminum sulfate and a 197
g / L aqueous sodium aluminate solution at a flow rate of 4.83 m
L / min and 3.33 mL / min were respectively injected. After the start of the injection, 120 minutes, 240 minutes, and 270 minutes, 500 mL
Was removed, and the gel product was filtered and sufficiently washed with ion-exchanged water. This was dried at 100 ° C. all day and night, and then fired at 600 ° C. in an air stream for 3 hours.

The NO reduction reaction was carried out in the same manner as in Example 1 except that the alumina catalyst prepared as described above was used, and propane was used instead of methanol as a reducing agent, and a reaction gas containing no steam was used. Are shown in Table 4 as Examples 2 to 4 together with the physical properties of the alumina catalyst.

[0054]

[Table 4]

From Table 4, it can be seen that the diameter is 60 compared to Examples 2 and 3.
The alumina catalyst shown in Example 4 having a large pore volume of not more than Å and a diameter of not more than 80 ° promotes the oxidation of propane, despite the fact that the entire pore volume and the surface area are small, It can be seen that the NOx reduction of NO. Is also proceeding with higher efficiency. According to these examples,
It can be confirmed that the pore volume of the alumina catalyst having a diameter of 60 ° or less and a diameter of 80 ° or less is an important factor that controls the NOx reduction efficiency.

Example 5 25 mL of an aqueous solution of aluminum sulfate having a concentration of 1344 g / L
Was diluted with 3000 mL of ion-exchanged water and 175 mL of an aqueous sodium aluminate solution having a concentration of 197 g / L, and then heated to 90 ° C. with stirring. to this,
134 g / L aluminum sulfate aqueous solution and concentration 19
A 7 g / L aqueous sodium aluminate solution was supplied at a flow rate of 4.83.
Each injection was performed at 3.33 mL / min. 180 minutes after the start of the injection, 500 mL was withdrawn, and the gel product was filtered and sufficiently washed with ion-exchanged water. this,
After drying all day and night at 100 ° C., it was baked at 600 ° C. in an air stream for 3 hours. Except for using the alumina catalyst prepared as described above, in the same manner as in Example 2, the results of the reduction reaction of NO were performed together with the physical properties of the alumina catalyst.
Table 5 shows Example 5.

Comparative Example 6 As a catalyst, an alumina catalyst having the characteristics shown in Table 5 (alumina KHS-46 manufactured by Sumitomo Chemical Co., Ltd., calcined at 700 ° C.)
The reduction and removal rate of NO was examined in the same manner as in Example 2 except for using. The results are shown in Table 5 as Comparative Example 6.

[0058]

[Table 5]

As is clear from Table 5, the alumina catalyst shown in Example 5 had a NO reduction removal rate and a propane reduction despite the smaller pore volume of 80 ° in diameter than the alumina catalyst shown in Comparative Example 6. Both oxidation rates are high. This is because the pore volume of 60 ° or less in the alumina catalyst shown in Example 5 is very large, so that the oxidation of propane is promoted even in a low temperature range, and the reduction and removal of NO also progress.

Example 6 (Experiment for removing NOx from actual diesel exhaust gas) An experiment using actual exhaust gas was conducted by separating a part of the exhaust gas of an Isuzu water-cooled 4-cycle in-line 4-cylinder diesel engine (direct injection type, 2771 cm ³ ). After removing the particulates with a SUS filter, the mixture was introduced into the catalyst layer. The catalyst performance was evaluated by measuring the exhaust gas before and after the catalyst layer with NOx, CO, CO ₂ , THC,
SOx and the like were quantified, and the determination was performed based on the NOx reduction rate. The operating conditions of the engine are 1300 rpm, load 10 kg · m
And At this time, the average composition of the exhaust gas is about 5% NOx.
00 ppm, CO about 350 ppm, CO ₂ about 4%, TH
C to about 500 ppm, SOx about 80 ppm, _{O 2} of about 16
%, H ₂ O about 6%. As described above, the NOx removal performance of the catalyst formed by processing the alumina prepared in Example 5 into a honeycomb shape was evaluated. The results are shown in Table 6.

[0061]

[Table 6]

From Table 6, it can be seen that when the alumina catalyst of the present invention was used, NOx in actual diesel exhaust gas containing about 6% of steam and about 80 ppm of sulfur oxides was hardly deteriorated for an extremely long time of 1300 hours or more. It is clear that the removal can be done with high efficiency without causing.

[0063]

As described in detail above, according to the present invention using a specific alumina catalyst, in an oxidizing atmosphere in which oxygen is excessively present, the efficiency of the exhaust gas, that is, almost completely depending on the reaction conditions, is reduced. NOx can be removed. Further, according to the present invention, even if a sulfur oxide is contained in the exhaust gas, a decrease in the activity of the specific alumina catalyst can be reduced. This particular alumina catalyst used in the present invention, encourage moderate oxidation of hydrocarbons or oxygen-containing organic compounds than the reaction between O ₂ and hydrocarbons or oxygen-containing organic compounds, NOx and hydrocarbons This is in order to preferentially promote the reaction with a compound or an oxygen-containing organic compound. As described above, the present invention efficiently removes NOx from exhaust gas from various facilities including diesel engine exhaust gas.
Can be removed and is of extremely high industrial value.

──────────────────────────────────────────────────続 き Continuing on the front page (74) Attorney of the above two patent attorneys Chikoshi Kubota (one outsider) (72) Inventor Mitsunori Tabata 1134-2 Gongendo, Satte City, Saitama Prefecture (72) Inventor Katsumi Miyamoto Saitama 1-111-17, Washinomiya, Washinomiya-cho, Kita-Katsushika-gun (72) Inventor Hiroshi Tsuchida 2-24-6-408, Kyomachi, Kawasaki-ku, Kawasaki-shi, Kanagawa (72) Inventor Yoshiaki Kaneda 1-1-1 Higashi, Tsukuba-shi, Ibaraki Prefecture Within the Institute of Engineering Technology (72) Inventor Motoi Sasaki 1-1-1 Higashi, Tsukuba City, Ibaraki Prefecture Examiner, Masahiro Inoue, Institute of Materials Science and Engineering, Institute of Industrial Science and Technology (56) References JP-A-7-24261 (JP, A) JP-A-6-205941 (JP, A) JP-A-6-198132 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/94 B01J 21/04 ZAB

Claims (1)

(57) [Claims] (1) In an oxidizing atmosphere in which excess oxygen is present, in the presence of a hydrocarbon or an oxygen-containing organic compound,
(1) The content of one or both of alkali metal and alkaline earth metal is 0.5 wt% or less and (2) diameter 6
Pore volume formed from pores of 0 ° or less is 0.06 cm
Nitrogen characterized by contacting an alumina catalyst having a pore volume of 0.1 cm ³ / g or more formed of pores having a diameter of not less than ³ / g and not more than 80 ° with an exhaust gas containing nitrogen oxides. A method for reducing and removing oxides.