JP2772117B2 - Manufacturing method of exhaust gas treatment catalyst - Google Patents

Description

The present invention relates to an exhaust gas containing nitrogen oxides (hereinafter abbreviated as NOx), carbon monoxide (CO), and hydrocarbons (hereinafter abbreviated as HC). The present invention relates to a method for producing a catalyst to be purified.

[Conventional technology]

In combustion exhaust gas emitted from gasoline engines such as automobiles, diesel engines such as trucks and buses, etc.
It contains harmful substances, such as NOx, CO, and HC, which are thought to cause photochemical smog. From the viewpoint of environmental protection, the development of a method to remove them is a serious and urgent social issue.

At present, Pt, Pd
In most cases, a noble metal such as the above is supported on an alumina coat layer on a refractory substrate.

However, the purification characteristics of the above catalyst are greatly influenced by the set air-fuel ratio of the engine. On the lean side, that is, on the lean side where the air-fuel ratio is large, the amount of oxygen increases after combustion, and the oxidizing action becomes active, so the reducing action becomes inactive. . On the other hand, since the oxidizing action becomes inactive on the rich side where the air-fuel ratio is small, these catalysts work effectively only at the theoretical air-fuel ratio (A / F) = 14.6 where the oxidation and reduction can be balanced with the current catalyst. Only. Therefore, in an automobile equipped with an exhaust gas purifying apparatus using a catalyst, feedback control is performed so as to detect the oxygen concentration in the exhaust system and maintain the air-fuel mixture near the stoichiometric air-fuel ratio.

[Issues to be solved]

On the other hand, automobiles are also required to have low fuel consumption,
It is known that, for that purpose, it is only necessary to burn an air-fuel mixture in excess of oxygen during normal running. However Then the air-fuel ratio becomes an oxygen-excess atmosphere leaner, HC of the harmful components in the exhaust gas, CO can be be removed oxide, NOx is hindered catalyst an active metal by O ₂ adsorbed on the catalyst bed Therefore, there is a problem that reduction and removal cannot be performed. For this reason, conventionally, it has not been possible to make the air-fuel mixture lean in an automobile that purifies advanced exhaust gas using a catalyst.

The present invention has been made in order to solve the above problems, and it is an object of the present invention to reduce and remove NOx even on the lean side, and to sufficiently remove all harmful components from a stoichiometric air-fuel ratio over a wide area on the lean side. It is an object of the present invention to provide a method for producing a catalyst for exhaust gas treatment that can be performed.

[Means for solving the problem]

The method for producing the exhaust gas treatment catalyst of the present invention includes the following steps. First, a slurry solution in which a binder and water are mixed with zeolite composed of a crystalline silicate described later carrying an active metal and a pH adjuster is further added to adjust the pH to about 4 and uniformly dispersed is prepared. Next, the obtained slurry solution is coated on an integrated carrier and baked.

The binder used in the above-mentioned preparation method is silica sol and alumina sol.
~ 60 parts, alumina sol 0.1-40 parts, additional water 5
It is preferable to mix at a ratio of 0 to 500 parts.

The zeolite used is in a dehydrated form and has a molar ratio of oxides of (1 ± 0.8) R ₂ O · [aM ₂ O ₃ · bAl ₂ O ₃ ] · ySiO ₂中 wherein R is an alkali metal ion and / or Or an ion or hydrogen of an organic nitrogen-containing compound, an ion of one or more elements of the group consisting of M: group VIII metal, rare earth element, titanium, vanadium, chromium, niobium, gallium, bismuth, tantalum, and antimony, a + b = 1 , a ≧ 0, b ≧ 0, y> 11 °, and the X-ray powder diffraction pattern is a crystalline silicate containing the reflection shown in Table A below. Both of these zeolites have a pore diameter of 5 to 10 °, which is slightly larger than the NO molecular diameter, and all the zeolites supporting a metal have a large NO adsorption amount.

Cu or Cu as active metal supported on zeolite
And Ca, Mg, Ba, Sr, Li, Na, K, B, Al, P, Sn, Sb, Si, Ti, Zn, V, Nb, F
At least one metal is selected from e, Co, Ni, Mn, La, Ce, Pr, Nd, Sm, and W. The metal can be supported by impregnating the H-type zeolite with the nitrate or chloride of each metal, or by immersing the metal in the aqueous solution of the cation on the zeolite by immersing it in an aqueous solution of 0.001 to 0.5 mol / metal salt. Examples of the method include ion exchange with ions. Further, a method of supporting the above-mentioned metal hydroxide or a complex product to which NH ₃ is coordinated on zeolite can also be used.

In the production method of the present invention, a method is employed in which after the active metal is supported on the zeolite, a slurry to which binder water has been added is coated on the integrated carrier. On the other hand, a method in which a slurry of a mixture of zeolite, a binder and water is coated on an integrated carrier, immersed in an aqueous solution of active metal after calcining, and the active metal is supported on zeolite, is a preferred method. Hard to say. The reason is that, in the latter case, when the active metal is finally supported on zeolite, the active metal may be supported on silica sol, alumina sol or carrier other than zeolite, and the exhaust gas treatment required by these active metals may be required. This is because there is a risk of inhibiting the reaction. Further, in the latter case, the active metal tends to be supported only on the surface, and the internal zeolite cannot be used effectively, so that the activity (particularly, denitration activity) is greatly reduced as compared with the former method. .

Further, as the amount of zeolite coated on the carrier increases, the catalytic activity at low temperatures improves, and it is desired that the amount of zeolite be 10 g / m ² , preferably 30 g / m ² or more per carrier surface area.

[Action]

The catalyst obtained by the production method of the present invention is uniformly covered with the zeolite supported on the active metal.

The catalyst produced according to the present invention has an action of sufficiently reducing NOx even under an excess of oxygen, and can simultaneously remove CO and hydrocarbons. At this time, CO and hydrocarbons react with NO to change into CO ₂ and H ₂ O, and can also be burned and removed by reacting with O ₂ .

 Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1] (a) Support of active metal on zeolite As a zeolite, the molar ratio was Na ₂ O · [0.6Fe ₂ O ₃ · 0.4Al ₂
O ₃ ] · 30 SiO ₂ (a silicate whose X-ray powder diffraction pattern is shown in Table A) is added to an aqueous copper acetate solution (Cu concentration 0.01 mol /), and the mixture is stirred at 20 ° C. for 24 hours. The above operation was repeated four times after further washing and filtration,
Copper ions were supported on the silicate by an ion exchange method. After ion exchange, washing is performed sufficiently, excess water is blown off, and then drying is performed at 90 ° C. to obtain catalyst powder A.

(B) Preparation of slurry Silica sol (Snowtex O ..
・ Silica content 20%) and alumina sol (alumina content 10%) are each 60 parts, 10 parts, and water 300 parts per 100 parts of catalyst powder.
The resulting mixture was mixed with nitric acid and adjusted to pH 4 with nitric acid to prepare a washcoat slurry.

(C) Coating and firing The monolithic honeycomb carrier made of cordierite is immersed in the above slurry solution, taken out, and then the excess slurry is blown off with compressed air, dried at 120 ° C. for about 30 minutes, dried, and further dried. Immerse in the solution. After repeating the above operation, a predetermined amount of catalyst powder (about 60 g / m ² substrate surface) was coated on the honeycomb carrier, and then fired at 600 ° C. for 3 hours in an electric furnace.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that the crystalline silicate used in Example 1 was replaced with a crystalline silicate having the following molar ratio (silicate having an X-ray diffraction chart shown in Table A). Obtain a powder.

Na ₂ O ・ Fe ₂ O ₃・ 25SiO ₂・ ・ ・ zeolite for catalyst powder B Na ₂ O ・ [0.6La ₂ O ₃・ 0.4Al ₂ O ₃ ] ・ 30SiO ₂・ ・ ・ zeolite for catalyst powder C Na ₂ O・ [0.3Cr ₂ O ₃・ 0.3Fe ₂ O ₃・ 0.4Al ₂ O ₃ ] ・ 32SiO ₂・ ・ ・ Zeolite for catalyst powder D Na ₂ O ・ [0.8Ga ₂ O ₃・ 0.2Al ₂ O ₃ ] ・ 33SiO ₂・ ・ ・ Zeolite for catalyst powder E Na ₂ O ・ [0.1Co ₂ O ₃・ 0.9Al ₂ O ₃ 】 ・ 30SiO ₂・ ・ ・ Zeolite for catalyst powder F Na ₂ O ・ [0.1Ti ₂ O ₃・ 0.9Al ₂ O ₃ ] · 31SiO ₂ ··· zeolite for catalyst powder G Na ₂ O · [0.1Nb ₂ O ₃ · 0.9 Al ₂ O ₃ ] · 30SiO ₂ · · · zeolite for catalyst powder H Na ₂ O · [0.05V ₂ O ₃ · 0.95 Al ₂ O ₃ ] · 30 SiO ₂ · · · zeolite for catalyst powder I Na ₂ O · [0.2Bi ₂ O ₃ · 0.8 Al ₂ O ₃ ] · 29 SiO ₂ · · · zeolite Na for catalyst powder J ₂ O ・ [0.05Ta ₂ O ₃・ 0.95Al ₂ O ₃ ] ・ 31SiO ₂・ ・ ・ zeolite for catalyst powder K Na ₂ O ・ [0.05Sb ₂ O ₃・ 0.95Al ₂ O ₃ ] ・ 30SiO ₂・ ・ ・Touch Powder L zeolite Na ₂ O · _{[0.1Ni 2 O 3 · 0.9Al 2 O} 3 ] · 30SiO ₂ ··· catalyst powder M zeolite further mordenite as a reference example (Si / Al ratio of 20) and Y-type zeolite (Si / Al ratio 30) to obtain catalyst powders N and O in the same manner as in Example 1.

[Example 3] In Example 1, "(a) Loading of active metal on zeolite", various metal ions were loaded by coion exchange in addition to loading of Cu ions. As the metal salts used, Cu ion is copper acetate, Fe ion is ferric chloride, Cr ion is chromium nitrate,
Co ion is cobalt nitrate, Mn ion is manganese acetate, Zn
Ion is zinc chloride, Mg ion is magnesium chloride, Ni ion is nickel acetate, Ca ion is calcium chloride, Li ion is lithium chloride, Na ion is sodium chloride, K ion is potassium chloride, Al ion is aluminum chloride, Sn
Ion is stannous chloride, Sb is antimony chloride, Ti
The ion is titanium tetrachloride, the V ion is vanadium trichloride,
Nb ion is niobium chloride, La ion is lanthanum chloride, Ce ion is cerium chloride, Pr ion is praseodymium chloride,
Nd ion is neodymium chloride, Sm ion is samarium chloride,
W ions used tungsten chloride.

Metal ion concentration Cu ion concentration 0.02 mol /, the metal ion concentration 0.02 mol / and then, the crystalline silicate used in the catalyst powder A _{[Na 2 O · (0.6Fe 2 O} 3 · 0.4Al 2 O 3) · 30SiO 2 ] Was immersed in the above aqueous solution to carry out co-ion exchange. The ion exchange conditions are the same as in Example 1. Each of the obtained catalyst powders is P, Q, R, S, T, U, V, W, X, Y, Z, a, b, c, d, e, f, g, h, i,
j, k, l.

Example 4 The crystalline silicate shown in Example 1 [Na ₂ O · (0.6Fe ₂ O ₃
・ 0.4Al ₂ O ₃ ) ・ 30SiO ₂ ] is protonated in a 4N aqueous solution of NH ₄ Cl at 80 ° C., dried and calcined at 550 ° C. to form H-form [H
_{2 O · (0.6Fe 2 O 3} · 0.4Al 2 O 3) · 30SiO 2 ].

This crystalline silicate is immersed in an aqueous cupric chloride solution to support copper by an impregnation method (Ca 1.0 mmol / g crystalline silicate). This catalyst powder is referred to as catalyst m.

Cupric chloride and boric acid, cupric chloride and phosphoric acid, cupric chloride and silicon tetrachloride, cupric chloride and barium chloride,
Cupric chloride and strontium chloride were co-impregnated by the above method. The obtained catalyst powder was converted into catalyst n [(Cu 1.0 mmol + B
1.0 mmol) / g crystalline silicate], catalyst o [(Cu 1.0 mmo
l + P 1.0 mmol) / g crystalline silicate], catalyst p [(Cu
1.0 mmol + Si 1.0 mmol) / g crystalline silicate], catalyst q
[(Cu 1.0 mmol + Ba 1.0 mmol) / g crystalline silicate],
The catalyst is r [(Cu 1.0 mmol + Sr 1.0 mmol) / g crystalline silicate].

Further, NH ₃ is added to the cupric chloride aqueous solution to form a copper-ammonia complex solution, and then the crystalline silicate shown in Example 1 is added to the above solution and stirred to cause the copper-ammonia complex to be supported on the crystalline silicate. . This catalyst powder is referred to as catalyst powder s.

[Test Example 1] The catalyst powders A to s obtained in the above Examples were coated on a honeycomb carrier by the method shown in Example 1 and catalyzed.
2.0 Attached to the exhaust of the engine, air-fuel ratio (A / F) 22.5,
The denitration activity was measured at an inlet gas temperature of 450 ° C.

 Table 1 shows the results.

Note that in Table 1, part of the chemical formula of the zeolite is ion-exchanged for simplicity (Na ₂ O) is omitted,
Only the basic skeleton is shown.

Test Example 2 A forced heating test was performed under the following conditions in order to examine the heat resistance of the catalyst powder A converted into a honeycomb catalyst.

After the above-mentioned forced heating test, the activity was evaluated under the conditions of Test Example 1. As a result, the denitration ratio was found to be 42%, indicating that the catalyst had heat resistance. The same forced heating test was performed on the honeycomb catalysts B to s, and after the activity evaluation, it was confirmed that the catalysts had heat resistance.

Comparative Example 1 A catalyst was prepared by a method different from that in Example 1. Molar ratio of zeolite is Na ₂ O ・ [0.6Fe ₂ O ₃・ 0.4Al ₂ O ₃ ] ・ 30SiO ₂
A binder and water were added to and mixed with the crystalline silicate represented by the formula, and then wash-coated on the honeycomb carrier. After firing, an aqueous solution of copper acetate (Cu concentration: 0.01 mol /) was supplied to the honeycomb to support Cu. This sample is designated as catalyst t. The activity of this catalyst was evaluated under the same conditions as in Test Example 1.

The activity results are shown in Table 2. The activity results of honeycomb catalyst A are also shown for reference.

[Effects of the Invention] The exhaust gas treatment catalyst obtained by the method of the present invention stably adheres a metal-supported zeolite having an action of directly taking in NOx onto an integrated monolith substrate, and includes a hydrocarbon and coexisting in exhaust gas. Carbon monoxide efficiently works to reduce NOx, and NOx can be removed even in an oxygen-excess atmosphere.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Yoshiaki Obayashi, Inventor 4-62-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Laboratory (72) Inventor Seito Suwa 4 Kannon-Shimmachi, Nishi-ku, Hiroshima-shi, Hiroshima No. 6-22, in the Hiroshima Laboratory, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-1-135540 (JP, A) JP-A-2-261545 (JP, A) JP-A-3-52644 (JP, A)

Claims (2)

(57) [Claims] In producing a monolith catalyst for treating an exhaust gas containing nitrogen oxides, carbon monoxide, hydrocarbons, etc., the molar ratio of the oxide in a dehydrated form is (1 ± 0.8) R.
₂ O · [aM ₂ O ₃ · bAl ₂ O ₃ ] · ySiO ₂ Rwherein, R is an alkali metal ion and / or an ion of an organic nitrogen-containing compound or hydrogen ion, M is a group VIII element, a rare earth element, titanium Ions of one or more elements of the group consisting of, vanadium, chromium, niobium, gallium, bismuth, tantalum, antimony,
a + b = 1, a ≧ 0, b ≧ 0, y> 11 °, and the active metal is supported on a crystalline silicate including the reflection shown in Table A, the X-ray powder diffraction diagram of which is shown in Table A in particular. A method for producing an exhaust gas treatment catalyst, which comprises mixing a binder and water with the mixture, adhering the obtained slurry solution to an integrated monolith substrate, and stabilizing the resulting mixture. 2. The active metal is copper or copper and calcium,
Magnesium, barium, strontium, lithium,
Sodium, potassium, boron, aluminum, phosphorus,
The claim 1 wherein at least one of tin, antimony, silicon, titanium, zinc, vanadium, niobium, iron, cobalt, nickel, manganese, lanthanum, cerium, praseodymium, neodymium, samarium, and tungsten is contained. Production method of exhaust gas treatment catalyst.