JPH0871373A - Removal of nitrogen oxide - Google Patents

Abstract

PURPOSE: To remove nitrogen oxide in combustion exhaust gas using a catalyst efficiently advancing the removal of NOx at relatively low reaction temp. and having a wide active temp. range. CONSTITUTION: Combustion exhaust gas containing oxygen is brought into contact with a catalyst containing indium and potassium as metals and alumina as a carrier at 300-550 deg.C in the coexistence of hydrocarbon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently removing nitrogen oxides (NOx) from combustion exhaust gas containing water vapor and oxygen, and more particularly to a catalyst containing indium, potassium and alumina. The present invention relates to a method for removing nitrogen oxides from the exhaust gas by using the method.

[0002]

2. Description of the Related Art From the viewpoint of environmental protection, removal of air pollutants is a major social issue. In particular, purification of combustion exhaust gas accompanying the expansion of industrial activities is an urgent issue at present.
The nitrogen compounds contained in the gas discharged from the automobile, which is a mobile generation source, and the factory, which is a fixed generation source, are harmful gases to the human body. Therefore, removal of NOx from the exhaust gas has been studied from various viewpoints, and some have already been put into practical use.

Examples thereof include (1) a three-way catalyst method for gasoline automobiles, and (2) a selective reduction method using ammonia for exhaust gas from a large facility emission source such as a boiler. However, the method (1) cannot be applied to diesel engine exhaust gas or gasoline lean burn engine exhaust gas containing oxygen, and the method (2) is toxic and often treats ammonia, which is treated as high-pressure gas, The equipment becomes huge because it is used, a small source,
It is especially difficult to apply to mobile sources.

Recently, a method for catalytically removing nitrogen oxides using a hydrocarbon as a reducing agent has been disclosed. For example, as using zeolites as catalysts, as shown in Proceedings 3E219 of the 70th Symposium on Catalysis, Proceedings 3H203 of the 61st Annual Meeting of the Chemical Society of Japan, and Japanese Patent Laid-Open No. 4-377738, Cu / ZSM-5 or the like is used. On the other hand, a method using an alumina-based catalyst is also disclosed in the 73rd Annual Meeting of the Catalyst Symposium 2A2, JP-A-5-38420 and the like. However, it is said that the former method has a problem in durability of the catalyst and NOx removal selectivity. Further, the latter method has a drawback in that a high reaction temperature is required although the durability of the catalyst is good. As described above, many methods for reducing and removing nitrogen oxides from exhaust gas containing oxygen have been attempted, but none that has sufficient performance for practical use has been found yet.

[0005]

An object of the present invention is to efficiently remove NOx even at a relatively low reaction temperature, which has been difficult to remove NOx with conventional alumina catalysts, and to use a catalyst with a wide activation temperature range. It is intended to provide a method for removing nitrogen oxides in combustion exhaust gas.

[0006]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, as a result of using a specific catalyst, NO from combustion exhaust gas containing oxygen.
A method for efficiently removing x was completed.

That is, the present invention is characterized in that a catalyst containing indium and potassium as metals and alumina as a carrier is brought into contact with combustion exhaust gas containing oxygen at a temperature of 300 to 550 ° C. in the presence of hydrocarbons. The present invention relates to a method for removing nitrogen oxides in the exhaust gas.

The catalyst is obtained by impregnating alumina with potassium using a potassium-containing solution and then impregnating indium with an indium-containing solution prepared separately from the potassium-containing solution. It relates to a method for removing nitrogen oxides, which is a catalyst supporting a metal.

Further, the catalyst contains indium of 0.1 to 20 wt% and potassium of 0.01 to 0.01 as metal oxides.
The present invention relates to a method for removing nitrogen oxides, which is characterized in that the catalyst is loaded with 2 wt%.

Hereinafter, the method of the present invention will be described in more detail.

The catalyst used in the method of the present invention is a catalyst containing indium and potassium as metals and alumina as a carrier.

Alumina used for the catalyst carrier is γ,
Although δ, η, θ, κ, ρ, χ, α, β type aluminas are known, γ, δ, η, θ, κ, ρ, χ, β type aluminas are preferably used, and particularly γ -Alumina is preferably used. The specific surface area is preferably 10 m ² / g or more, more preferably 50 m ² / g or more, especially 50 to 10
00 m ² / g is preferable. Specific surface area of alumina is 10m
If it is less than ² / g, the contact area between the exhaust gas and alumina becomes small, and good NOx removal cannot be performed. When high heat resistance is required, a mixture of alumina with cordierite, mullite or the like may be used as a carrier.

The active metals used in the catalyst are indium and potassium. As the starting materials for indium and potassium, their nitrates, sulfates, chlorides and the like are used.
Nitrate is preferably used.

The method of supporting the active metal is not particularly limited. For example, an impregnation method, a coprecipitation method, a deposition method, a kneading method and the like are known, but the impregnation method is preferably used in the present invention.

As the impregnation method, the carrier is immersed in the impregnating solution at room temperature or above room temperature to maintain the condition that the desired metal is sufficiently impregnated into the carrier. The amount and temperature of the impregnating solution can be appropriately adjusted so that a desired amount of metal is supported. When supporting two or more metals as the supporting metal, a mixed solution in which two or more metals are mixed is used to impregnate the carriers with the metals at the same time, or two or more metal solutions are separately prepared. Prepared by the method described above, and the solution is used to successively impregnate the carrier with the metal. In the present invention, either method may be used, but the latter method is preferable, in particular, a potassium-containing solution and an indium-containing solution are separately prepared, and alumina is first impregnated with potassium using the potassium-containing solution, and then the indium-containing solution is used. Preferred is a method of impregnating indium with and supporting two kinds of metals.

Further, it is preferable to carry out firing at 400 to 900 ° C. after supporting the active metal on alumina.

The amount of indium supported as an oxide is in the range of 0.1 to 20 wt%, preferably 5 to 15 wt%, based on the total weight of the catalyst. In addition, the amount of supported potassium is, as its oxide, 0.
It is in the range of 01 to 2 wt%, preferably 0.05 to 0.5 wt%.

The catalyst used in the method of the present invention is obtained by supporting the above-mentioned metal on alumina, and then using, for example, an inorganic oxide such as silica / alumina or clay as a binder, spherical, columnar,
It may be molded into a suitable shape such as a honeycomb shape, or may be molded by adding the binder before supporting the above metal on alumina, and then supporting the metal. In any case, it is not particularly limited.

The hydrocarbon used in the present invention is a compound composed of carbon and hydrogen, such as olefins, paraffins, cyclic compounds and hydrocarbons containing these compounds, which are usually called. It is preferably volatile and gaseous at the processing temperature of the present invention. More preferably, it is at least one hydrocarbon selected from olefins having 1 to 6 carbon atoms, paraffins and naphthenes. Specific examples include methane, ethane, propane, butane, pentane, hexane, ethylene, propylene, butylene, pentene, hexene, cyclopropane,
Hydrocarbons such as cyclobutane, cyclopentane, cyclohexane and cyclohexene can be used. Further, petroleum-based hydrocarbons such as gasoline, kerosene, and light oil can be used.

The amount of hydrocarbon added is 1 with respect to the combustion exhaust gas.
0 to 10000 ppm, preferably 1000 to 5000
It is ppm.

The oxygen-containing combustion exhaust gas (process gas) treated by the method of the present invention is a combustion exhaust gas containing oxygen at least 0.1 vol% or more,
It is emitted from a normal internal combustion engine, boiler, or the like. The present invention is particularly effective for exhaust gas containing a large amount of oxygen, such as exhaust gas from a diesel engine or a lean-burn gasoline engine.

The processing temperature according to the present invention is 300 to 550 ° C.
In the range, preferably 350 to 550 ° C. If this temperature is lower than 300 ° C, NOx cannot be removed.
When the temperature is higher than 0 ° C, the coexisting hydrocarbon causes combustion, and N
There is a drawback that the removal rate of Ox is low. In the present invention, the contact time between the catalyst and the processing gas is not limited.

When carrying out the method of the present invention, the combustion exhaust gas heated to a predetermined temperature by a cooler or the like is introduced into a reaction treatment apparatus (treatment section) filled with a catalyst, and the predetermined hydrocarbon contained in a special tank is removed. It may be added to the treatment section or an appropriate line before it. When the exhaust gas is not at the predetermined temperature, the treatment section may be heated. When the present invention is applied to exhaust gas from an engine, a part of fuel oil such as gasoline contained in an existing fuel tank is bypassed to the engine,
It may be added to the treatment section provided on the outlet side of the engine, or may be added to the treatment section after undergoing a reforming treatment or the like in the reforming section provided in the bypass.

[0024]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 (Preparation of catalyst) γ-alumina (specific surface area 100 m ² /
g) was dispersed in a solution of 0.1N potassium nitrate, stirred for 6 hours, filtered, and thoroughly washed with ion-exchanged water. The obtained product was dried under reduced pressure, further dried at 110 ° C., and baked at 500 ° C. for 2 hours. Further, this was dispersed in a solution of 0.1N indium nitrate, stirred for 6 hours, filtered, and thoroughly washed with ion-exchanged water. The obtained product was dried under reduced pressure, further dried at 110 ° C., and calcined at 500 ° C. for 2 hours to obtain a catalyst. The resulting catalyst contained 10 wt% indium and 0.2 wt% potassium as metal oxides.

(Evaluation of activity) The catalyst obtained by the above catalyst preparation was filled in a reaction treatment device having a capacity of 5 cm ³ , and NOx was 1000 ppm and oxygen was 10 v at a predetermined reaction temperature.
A gas containing ol% and 7 wt% of water was introduced at a flow rate: space velocity (SV) = 35000 h ⁻¹ to cause a catalytic reaction, and the NOx removal rate by the catalytic reaction was determined. Before the contact reaction, propylene as a hydrocarbon was added to the above gas at about 1000 ppm. The obtained results are shown in FIG.

Comparative Example 1 The activity was evaluated in the same manner as in Example 1 except that γ-alumina not supporting indium and potassium (specific surface area 100 m ² / g) was used as a catalyst. The obtained results are shown in FIG.

Comparative Example 2 γ-alumina (specific surface area 100 m ² / g) was dispersed in a 0.1N cobalt nitrate solution, stirred for 6 hours, filtered, and thoroughly washed with ion-exchanged water. The obtained product was dried under reduced pressure 11
It was further dried at 0 ° C and calcined at 500 ° C for 2 hours to obtain a catalyst. The obtained catalyst contains 1 cobalt as a metal oxide.
It contained 0 wt%. The activity was evaluated in the same manner as in Example 1 except that the catalyst was used. The obtained results are shown in FIG.

Comparative Example 3 γ-alumina (specific surface area 100 m ² / g) was dispersed in a 0.1N indium nitrate solution, stirred for 6 hours, filtered, and thoroughly washed with ion-exchanged water. The obtained product was dried under reduced pressure 1
It was further dried at 10 ° C and calcined at 500 ° C for 2 hours to obtain a catalyst. The obtained catalyst contained 10 wt% of indium as a metal oxide. The activity was evaluated in the same manner as in Example 1 except that the catalyst was used. The obtained results are shown in FIG.

Comparative Example 4 γ-alumina (specific surface area 100 m ² / g) was dispersed in a 0.1N potassium nitrate solution, stirred for 6 hours, filtered, and thoroughly washed with ion-exchanged water. The obtained product was dried under reduced pressure 11
It was further dried at 0 ° C and calcined at 500 ° C for 2 hours to obtain a catalyst. The obtained catalyst contained 0.2 wt% of potassium as a metal oxide. The activity was evaluated in the same manner as in Example 1 except that the catalyst was used. The obtained results are shown in FIG.

As is apparent from FIG. 1, the catalyst according to the present invention obtained in Example 1 has a high NOx removal activity in a wide range of reaction temperatures of 300 to 550 ° C., and particularly at a relatively low reaction temperature. A very high NOx removal activity was obtained as compared with the catalysts obtained in other Comparative Examples 1 to 4. Therefore, according to the method of the present invention using the catalyst according to the present invention, NOx can be efficiently removed from the combustion exhaust gas containing oxygen in a wide range of reaction temperatures of 300 to 550 ° C. NO in catalyst
It was found that NOx can be efficiently removed even at a relatively low reaction temperature where removal of x was difficult.

[0032]

As described above, according to the present invention,
In a wide range of reaction temperatures of 300 to 550 ° C., the catalytic activity is not significantly reduced, and NOx can be efficiently removed from oxygen-containing combustion exhaust gas. Therefore,
By adopting the above-mentioned method of the present invention, it becomes possible to efficiently remove NOx even at a relatively low reaction temperature where it was difficult to remove NOx with the conventional alumina-based catalyst.

[Brief description of drawings]

FIG. 1 is a graph showing NOx removal activity of catalysts of Examples and Comparative Examples.

Claims (3)

[Claims] 1. A catalyst containing indium and potassium as metals and alumina as a support, at a temperature of 300 to 5.
A method for removing nitrogen oxides from exhaust gas, which comprises contacting combustion exhaust gas containing oxygen at 50 ° C. in the presence of hydrocarbons. 2. The catalyst is obtained by impregnating alumina with potassium using a potassium-containing solution and then impregnating indium with an indium-containing solution prepared separately from the potassium-containing solution. The method according to claim 1, wherein the catalyst is a metal-supported catalyst. 3. The catalyst comprises indium as a metal oxide in an amount of 0.1 to 20 wt% and potassium in an amount of 0.01 to 2 w.
The catalyst loaded with t% is characterized in that
The described method.