JP4291421B2 - Exhaust gas purification catalyst - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for the purification of exhaust gases containing high concentrations of oxygen, in particular exhaust gases from diesel engines. More specifically, the present invention relates to a method and apparatus that can reduce nitrogen oxide contained in exhaust gas with high efficiency.
[0002]
[Prior art]
In order to reduce nitrogen oxides contained in exhaust gas in the presence of high-concentration oxygen, zeolite formed by ion-exchange of transition metals is used as a catalyst, and the amount of reducing agent is less than the theoretical reaction amount with oxygen in exhaust gas. A method for reducing nitrogen oxides by adding NO is proposed (Japanese Patent Laid-Open No. 63-283727). However, in this method, since the optimum activation temperature of the catalyst is as high as 400 to 600 ° C., the reduction rate of nitrogen oxide is considerably low when the exhaust gas is in a low temperature range of 200 to 400 ° C., such as when starting the engine.
[0003]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a method and an apparatus that can reduce nitrogen oxide contained in exhaust gas over a wide temperature range with high efficiency.
[0004]
[Means for Solving the Problems]
As a result of earnest research, the inventor of the present invention, after contacting exhaust gas at 200 to 600 ° C. with an upstream catalyst composed of platinum ion exchanged zeolite, further sodium, potassium, magnesium, calcium, barium, manganese, iron and zinc Surprisingly, the reducing agent is less than the theoretical amount of reaction with oxygen in the exhaust gas by contacting a downstream catalyst consisting of zeolite or alumina exchanged with ions of one element selected from the group consisting of The inventors have found that nitrogen oxides can be reduced with high efficiency over a wide temperature range even if only the amount exists, and have proposed the exhaust gas purification method of the present invention.
[0005]
That is, the exhaust gas purification method of the present invention uses, as an exhaust gas purification catalyst, ions of one element selected from the group consisting of platinum ion-exchanged zeolite and sodium, potassium, magnesium, calcium, barium, manganese, iron and zinc. First, after contacting the exhaust gas with platinum ion-exchanged zeolite (hereinafter referred to as “first catalyst”), the exhaust gas is sodium, potassium, magnesium, calcium, barium, manganese, It is characterized by contacting with zeolite or alumina (hereinafter referred to as “second catalyst”) exchanged with ions of one element selected from the group consisting of iron and zinc . Preferably, after contacting the exhaust gas with platinum ion exchanged zeolite, the zeolite exchanged with ions of one element selected from the group consisting of sodium, potassium, magnesium, calcium, barium, manganese, iron and zinc, or Prior to contacting the alumina, a reducing agent is added.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
First catalyst Platinum ion exchanged zeolite. This is a zeolite prepared by replacing the ion exchange group of the zeolite with platinum ions.
[0007]
The zeolite used in the present invention has the general formula:
_{xM 2 / n O · Al 2} O 3 · ySiO 2 · zH 2 O
(Where n is the valence of the cation M, x is a number in the range of 0.8 to 1.2, y is a number of 2 or more, and z is a number of 0 or more). Crystalline aluminosilicate. Various synthetic products are known as well as natural products, but any zeolite can be used in the present invention. The silica / alumina molar ratio is preferably 10 or more. Ferrierite, Y-type, mordenite, ZSM-5, ZSM-11 and the like are typical ones. A preferred zeolite is ZSM-5. Zeolite may be used as it is, but may be NH ₄ type or H type. Further, it may contain a cation such as alkali metal or alkaline earth metal. The structure preferably has a dimensional or three-dimensional channel inside the crystal.
[0008]
In order to perform ion exchange with platinum ions, for example, zeolite is immersed in a solution containing platinum ions and stirred at 20 to 100 ° C. for several hours to several tens of hours. Platinum ions can be supplied in the form of, for example, dinitrodiaminoplatinum. The amount of platinum ions contained in the zeolite is preferably in the range of 0.1 to 5 wt% (Pt) with respect to the zeolite. After the ion exchange, the produced slurry is subjected to solid-liquid separation, the zeolite cake is washed with ion exchange water (preferably pure water), and then dried at 100 to 150 ° C. in the atmosphere for 2 to 3 hours. In addition, you may perform repeatedly the ion exchange operation which immerses a zeolite cake in the solution containing a platinum ion again. Prior to disposing the finished catalyst in the exhaust line, calcination is preferably performed at 400 to 600 ° C. for 3 to 5 hours as an activation treatment. The atmosphere may be oxidizing, reducing or inert.
[0009]
The shape of the catalyst is not particularly limited. Therefore, it can be pulverized and used as a powder, or it can be further shaped into a certain shape (for example, pellets) by adding a binder, or on a fire-resistant substrate such as a honeycomb (for example, cordierite) You may apply to.
[0010]
Second catalyst Element selected from the group consisting of indium, gallium, copper, cobalt, sodium, potassium, magnesium, calcium, barium, manganese, iron, nickel, zinc and hydrogen (hereinafter referred to as "M") Zeolite exchanged with ions or alumina.
[0011]
The same zeolite as the first catalyst can be used. In addition, the exchange operation and catalyst preparation operation of each ion of indium, gallium, copper, cobalt, sodium, potassium, magnesium, calcium, barium, manganese, iron, nickel, zinc and hydrogen are the same as in the case of preparing the first catalyst. Can be implemented.
[0012]
Indium ions can be supplied, for example, in the form of indium nitrate (In (NO ₃ ) ₃ ) or indium chloride (InCl ₃ ). Gallium ions can be supplied, for example, in the form of gallium nitrate (Ga (NO ₃ ) ₃ ), gallium chloride (GaCl ₃ ), or gallium sulfate (Ga ₂ (SO ₄ ) ₃ ). Copper ions can be supplied, for example, in the form of copper nitrate (Cu (NO ₃ ) ₂ ), copper acetate (Cu (CH ₃ COO) ₂ ), or copper sulfate (CuSO ₄ ). Cobalt ions can be supplied, for example, in the form of cobalt nitrate (Co (NO ₃ ) ₂ ) or cobalt acetate (Co (CH ₃ COO) ₃ ). Sodium ion can be supplied in the form of, for example, sodium nitrate, sodium chloride, or sodium sulfate. Potassium ions can be supplied, for example, in the form of potassium nitrate or potassium chloride. Magnesium ions can be supplied, for example, in the form of magnesium nitrate or magnesium sulfate. Calcium ions can be supplied, for example, in the form of calcium nitrate or calcium chloride. Barium ions can be supplied, for example, in the form of barium nitrate or barium hydroxide. Manganese can be supplied, for example, in the form of manganese nitrate or manganese sulfate. Iron ions can be supplied in the form of, for example, iron nitrate or iron (II) sulfate. Nickel ions can be supplied, for example, in the form of nickel nitrate or nickel sulfate. Zinc ions can be supplied, for example, in the form of zinc nitrate or zinc sulfate. The amount of M ions contained in the zeolite is preferably in the range of 1 to 6 wt% with respect to the zeolite.
[0013]
Reducing agent Ammonia, carbon monoxide or hydrocarbon may be used, but hydrocarbon is preferred. As for the reducing agent composed of hydrocarbon, methane, ethane, ethylene, propane, propylene, butane, butylene, butene, acetylene, isoprene and the like are gaseous, and liquids are pentane, hexane, oxane, Single component systems such as heptane, benzene, toluene and xylene, and mineral oil systems such as gasoline, kerosene, heavy oil and light oil can be used. These may be used alone or in combination. The method of the present invention is advantageous because light oil can be used when purifying exhaust gas from a diesel engine.
[0014]
The exhaust gas contains unburned and incompletely burned products such as fuel, that is, hydrocarbons and particulates, which are also effective as reducing agents. Therefore, it is not always necessary to add the reducing agent from the outside. However, normally, when a reducing agent is added to the exhaust gas that has passed through the first catalyst and then brought into contact with the second catalyst, the reduction rate of nitrogen oxides increases considerably.
[0015]
The amount of hydrocarbon varies depending on the specific type of hydrocarbon used, but is usually 1 to 4 times the discharge weight of nitrogen oxides.
[0016]
Exhaust gas purification apparatus To carry out the exhaust gas purification method of the present invention, a first catalyst made of platinum ion exchange zeolite is arranged on the upstream side with respect to the flow of the exhaust gas, sodium on the downstream side , A second catalyst made of zeolite or alumina exchanged with ions of one element selected from the group consisting of potassium, magnesium, calcium, barium, manganese, iron and zinc is disposed. In a preferred embodiment, a reducing agent injection means is provided between the first catalyst and the second catalyst so as to communicate with the exhaust pipe and to inject the reducing agent therein.
[0017]
In one example, as shown in FIG. 1, casings are sequentially formed in the exhaust pipe 4, specifically between the exhaust manifold 5 and the exhaust muffler 6, sequentially from the upstream with respect to the flow of exhaust gas emitted from the engine 9. An exhaust gas purification device 1 comprising a first catalyst (powdered) 2 and a second catalyst (powdered) 3 is provided in a form housed in such an outer cylinder, and further, an exhaust pipe 4 And a reducing agent injection means 7 for injecting a reducing agent (gaseous state) between the first catalyst 2 and the second catalyst 3. The reducing agent is pumped by the pump 8 and is supplied into the exhaust pipe 4 from the injection nozzle via a regulating valve (not shown).
[0018]
The first catalyst zeolite and the second catalyst zeolite are preferably arranged such that the respective amounts are in a ratio of 1: 1.
[0019]
The present invention relates to an upstream catalyst comprising platinum ion exchanged zeolite; zeolite or alumina exchanged with ions of one element selected from the group consisting of sodium, potassium, magnesium, calcium, barium, manganese, iron and zinc And a downstream catalyst comprising: a catalyst system for purifying exhaust gas.
[0020]
【Example】
Preparation of catalyst (production of first catalyst)
Zeolite (ZSM-5, SiO ₂ / Al ₂ O ₃ = 30, 20 g) was immersed in a solution obtained by dissolving dinitrodiaminoplatinum (0.53 g) in water (100 ml) and kept at 80 ° C., Stir well for 2 days to replace the ion exchange groups of the zeolite with platinum ions. Thereafter, the obtained slurry was washed with pure and separated into solid and liquid, and the obtained zeolite cake was dried at 100 ° C. for 2 hours in the atmosphere, and subsequently calcined at 500 ° C. for 5 hours in the atmosphere. Thereafter, the fired product was pulverized to obtain a powder having a particle size of 150 to 100 mesh. The platinum content was 1.5 wt%.
[0021]
(Production of second catalyst)
Production of gallium ion exchange catalyst Zeolite (ZSM-5, SiO ₂ / Al ₂ O ₃ = 30, ₂₀ g) was dissolved in a solution of gallium nitrate (3.0 g) dissolved in water (100 ml). While being immersed and kept at 60 ° C., the mixture was sufficiently stirred for 2 days to replace the ion exchange groups of the zeolite with gallium ions. Thereafter, the obtained slurry was washed with pure and separated into solid and liquid, and the obtained zeolite cake was dried at 100 ° C. for 2 hours in the atmosphere, and subsequently calcined at 500 ° C. for 5 hours in the atmosphere. Thereafter, the fired product was pulverized to obtain a powder catalyst having a particle size of 150 to 100 mesh.
[0022]
Production of indium ion exchange catalyst A powder catalyst was produced in the same manner as in the production of gallium ion exchange catalyst except that indium nitrate (4.9 g) was used instead of gallium nitrate. . The content of indium ions was 3 wt%.
[0023]
Production of copper ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that copper nitrate (3.6 g) was used instead of gallium nitrate. The copper ion content was 3.8 wt%.
[0024]
Preparation of cobalt ion exchange catalyst A powder catalyst was prepared in the same manner as in the preparation of the gallium ion exchange catalyst except that cobalt nitrate (3.4 g) was used instead of gallium nitrate. The cobalt ion content was 3.5 wt%.
[0025]
Production of hydrogen ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst, except that an aqueous solution containing 20 wt% ammonium nitrate was used.
[0026]
Production of sodium ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that sodium nitrate (7.9 g) was used instead of gallium nitrate. The content of sodium ions was 2.1 wt%.
[0027]
Preparation of potassium ion exchange catalyst A gallium ion exchange catalyst was prepared except that potassium nitrate (5.3 g) was used instead of gallium nitrate. The content of potassium ions was 1.9 wt%.
[0028]
Production of magnesium ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that magnesium nitrate (7.3 g) was used instead of gallium nitrate. The magnesium ion content was 2.0 wt%.
[0029]
Production of calcium ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that calcium nitrate (5.2 g) was used instead of gallium nitrate. The content of calcium ions was 1.9 wt%.
[0030]
Production of barium ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that barium nitrate (3.0 g) was used instead of gallium nitrate. The barium ion content was 2.0 wt%.
[0031]
Production of manganese ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that manganese nitrate (4.3 g) was used instead of gallium nitrate. The manganese ion content was 2.1 wt%.
[0032]
Production of iron ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that iron nitrate (4.3 g) was used instead of gallium nitrate. The iron ion content was 2.0 wt%.
[0033]
Production of nickel ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that nickel nitrate (4.2 g) was used instead of gallium nitrate. The content of nickel ions was 2.0 wt%.
[0034]
Production of zinc ion exchange catalyst A powder catalyst was produced in the same manner as in the production of the gallium ion exchange catalyst except that zinc nitrate (4.0 g) was used instead of gallium nitrate. The zinc ion content was 2.0 wt%.
[0035]
Test apparatus The test was performed using the test apparatus shown in FIG. The reaction tube 1 is provided with a first catalyst, and the reaction tube 2 is provided with a second catalyst.
In addition, the apparatus in which the 1st catalyst was not arrange | positioned was comprised separately as an apparatus of a comparative example.
[0036]
Test conditions Exhaust gas from a diesel engine was assumed and the exhaust gas was circulated through the exhaust gas purification device under the following conditions to measure the reduction rate of nitrogen oxides.
Gas chemical composition NO: 1000ppm
C ₂ H ₄ : 1000 ppm
O ₂ : 5%
He: Remaining space velocity (GHSV) 18,000 hr ⁻¹
[0037]
Evaluation FIG. 3 is a graph showing changes in the reduction rate of nitrogen oxides at various exhaust gas temperatures when the exhaust gas purifying apparatus of the example according to the method of the present invention is used. In FIG. 3, Pt & Ga, Pt & In, Pt & Cu, Pt & Co, and Pt & H are the first catalyst is a platinum ion exchange zeolite catalyst and the second catalyst is a gallium ion exchange zeolite catalyst, an indium ion exchange zeolite catalyst, and a copper ion exchange zeolite catalyst, respectively. , Cobalt ion exchange zeolite catalyst, hydrogen ion exchange zeolite catalyst. FIG. 4 is a diagram showing a change in the reduction rate of nitrogen oxides when using an exhaust gas purification apparatus in which only the second catalyst is provided as a comparative example. In FIG. 4, Ga, In, Cu, Co , H refers to the catalyst as in FIG. 3 and 4, the horizontal axis represents the catalyst inlet temperature of exhaust gas.
[0038]
FIG. 5 is a graph showing changes in nitrogen oxide reduction rates of different catalysts at various exhaust gas temperatures. In FIG. 5, Pt & Mn, Pt & Ni, Pt & Zn, Pt & Fe, Pt & Na, Pt & Mg, Pt & Ba, Pt & Ca, and Pt & K are the first catalyst is a platinum ion exchange zeolite catalyst, and the second catalyst is a manganese ion exchange zeolite catalyst and nickel ion exchange, respectively. Zeolite catalyst, zinc ion exchange zeolite catalyst, iron ion exchange zeolite catalyst, sodium ion exchange zeolite catalyst, magnesium ion exchange zeolite catalyst, barium ion exchange zeolite catalyst, calcium ion exchange zeolite catalyst, potassium refers to ion exchange zeolite catalyst.
[0039]
FIG. 6 is a diagram showing changes in the reduction rate of nitrogen oxides when using an exhaust gas purification apparatus in which only the second catalyst is disposed as a comparative example. In FIG. 6, Mn, Ni, Zn, Fe , Na, Mg, Ba, Ca and K indicate catalysts as in FIG. 5 and 6, the horizontal axis represents the catalyst inlet temperature of the exhaust gas.
[0040]
Comparing FIGS. 3 and 4 and FIGS. 5 and 6, it can be seen that when the first catalyst is disposed, the reduction rate of the nitrogen oxides is improved as compared with the case where the first catalyst is not disposed. In particular, it can be seen that when the temperature of the exhaust gas at the catalyst inlet is in a low temperature range of 200 to 400 ° C., the reduction rate of nitrogen oxides is dramatically improved.
[0041]
【The invention's effect】
According to the method of the present invention, even when the exhaust gas is in a low temperature range of 200 to 400 ° C., it is possible to prevent the nitrogen oxide contained in the exhaust gas from being released into the atmosphere as it is.
[Brief description of the drawings]
FIG. 1 is a schematic view of one apparatus capable of carrying out the exhaust gas purification method of the present invention.
FIG. 2 is a schematic view of an apparatus used in Examples.
FIG. 3 is a graph showing changes in the reduction rate of nitrogen oxides when the exhaust gas purifying apparatus (FIG. 1) of the example according to the method of the present invention is used.
FIG. 4 is a graph showing a change in the reduction rate of nitrogen oxide when an exhaust gas purifying apparatus provided with only a second catalyst is used as a comparative example.
FIG. 5 is a graph showing changes in the reduction rate of nitrogen oxides when the exhaust gas purifying apparatus (FIG. 1) of the example according to the method of the present invention is used.
FIG. 6 is a graph showing a change in the reduction rate of nitrogen oxide when an exhaust gas purifying apparatus provided with only a second catalyst is used as a comparative example.
[Explanation of symbols]
1: Exhaust gas purification device 2: First catalyst (platinum ion exchange zeolite)
3: second catalyst (zeolite or alumina exchanged with ions of an element selected from the group consisting of indium, gallium, copper, cobalt, sodium, potassium, magnesium, calcium, barium, manganese, iron, nickel, zinc and hydrogen )
4: exhaust pipe line, 5: exhaust manifold, 6: exhaust muffler 7: reducing agent injection means, 8: pump, 9: engine

Claims (5)

After contacting exhaust gas at 200 to 500 ° C. with an upstream catalyst made of platinum ion exchanged zeolite, zeolite exchanged with ions of one element selected from the group consisting of sodium, magnesium, calcium, and barium, or The downstream catalyst made of alumina is contacted in the presence of a reducing agent. At that time, the amount of platinum ions contained in the upstream catalyst is 0.1 to 5 wt% with respect to zeolite, and the ions of the downstream catalyst An exhaust gas purification method, wherein the amount of is 1 to 6 wt% with respect to zeolite.   The method according to claim 1, wherein the reducing agent is added after the exhaust gas is brought into contact with the upstream catalyst and before being brought into contact with the downstream catalyst.   The method according to claim 2, wherein hydrocarbon, gasoline, kerosene, or light oil is used as the reducing agent and is used for treating exhaust gas from a diesel engine. A combination of an upstream catalyst composed of platinum ion exchanged zeolite and a downstream catalyst composed of zeolite or alumina exchanged with ions of one element selected from the group consisting of sodium, magnesium, calcium, and barium The amount of platinum ions contained in the upstream catalyst is 0.1 to 5 wt% with respect to the zeolite, and the amount of ions in the downstream catalyst is 1 to 6 wt% with respect to the zeolite. A catalyst system for exhaust gas purification at 200 to 500 ° C. Inside the exhaust pipe, with respect to the flow direction of the exhaust gas, from the upstream side, one upstream catalyst made of platinum ion-exchanged zeolite and one kind selected from the group consisting of sodium, magnesium, calcium, and barium A downstream catalyst made of zeolite or alumina exchanged with elemental ions, wherein the amount of platinum ions contained in the upstream catalyst is 0.1 to 5 wt% with respect to the zeolite, The amount of ions in the downstream catalyst is 1 to 6 wt% with respect to the zeolite, and a reducing agent injection means for injecting the reducing agent into the exhaust pipe line between both catalysts is provided. and wherein, 200 to 500 ° C. of the exhaust gas purifying apparatus.

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