JPH044045A - Catalyst for processing exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a ternary catalyst having high activity even in the presence of a large amt. of oxygen by using crystalline silicate having a specified composition and crystal structure and allowing copper and other specified active metal to coexist. CONSTITUTION:The crystalline silicate used has the x-ray diffraction property as shown in Table (A) and its composition is expressed by the molar ratio of oxides in a dehydrated state as [(1.0+ or -0.8)R2O.>=aM2O3.bAl2O3].ySiO2, wherein ar is alkali metal and/or hydrogen, M is group VIII metal or rare earth metal, a+b=1, a>=0, b>=0, y>11. Then copper and specified metal such as Mg, Ba, etc., are made to coexist in this silicate. Thereby, Cu on the silicate activates CO and hydrocarbon to effect the reaction of these gases with NO to remove NOX. Moreover, coexistence of other metal improves heat resistance of Cu and selectivity of denitration reaction is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention purifies exhaust gas containing nitrogen oxides (hereinafter abbreviated as NOx), carbon oxides (CO), and hydrocarbons (hereinafter abbreviated as HC). related to catalysts.

[Conventional technology]

There is N in the combustion exhaust gas emitted from gasoline engines such as automobiles, diesel engines such as trucks and buses, etc.
It contains toxic substances such as Ox, CD, and HC that are said to cause photochemical smog, and from the standpoint of environmental conservation, developing methods for removing them is a serious and urgent social issue.

Methods for removing NOx from exhaust gas include adsorption method, oxidation absorption method,
Although there are catalytic reduction methods, the catalytic reduction method, which does not require post-treatment, is said to be economically and technically advantageous. This catalytic reduction method reduces NOx by passing through a catalyst in the presence of reducing gas.
This method converts nitrogen into harmless nitrogen, and can be divided into three methods depending on the type of reducing agent.

That is, a so-called non-selective reduction method in which a reducing gas such as hydrogen, carbon oxide, or hydrocarbon is added and brought into contact with a catalyst;
This is a so-called selective reduction method in which a reducing gas such as ammonia is added and brought into contact with a catalyst. The former has the disadvantage that it requires a large amount of reducing agent because the NOx removal reaction proceeds after the reaction between the oxygen coexisting in the gas and the reducing agent. When a reducing agent such as a hydrocarbon is already contained in an amount equal to or more than the same mole of oxygen, it is more advantageous to purify NOx in exhaust gas by a non-selective reduction method, and the catalyst for purifying NOx in automobile exhaust gas is a non-selective reduction method. Products for reaction have been put into practical use.

Automobile exhaust gas has a gas composition as shown in Figure 1 when no catalyst is used, but it contains Pt, Rh (active metal bodies) /Al2
When a three-way catalyst such as O3 (carrier)/cordierite (honeycomb base material) is used, the gas composition will be as shown in Figure 2, and the three components NOx, CD, and HC will be purified near the stoichiometric air-fuel ratio. ing. Engine combustion exhaust gas at the stoichiometric air-fuel ratio has approximately the following composition.

CO: 0.3-1.0%, NO: 0.05-0.15%
, H2O: about 13%, H,: 0.1-0.3%, H[:
:0.03~0.08%, S02: Approx. 0.002%, 0
□: 0.2 to 0.5%, CO3: approximately 12% [Problem to be solved by the invention] Using the above-mentioned three-way catalyst, which has been put into practical use for purifying the exhaust gas of automobile engines. In this case, oxygen is consumed by the oxidation reaction, and the NO reduction reaction proceeds in a state where the oxygen concentration is considerably low. Therefore, the current three-way catalyst is effective only near the stoichiometric air-fuel ratio (14,6), and it is difficult to reduce NOx in the high air-fuel ratio range where the combustion consumption rate can be low.

On the other hand, in order to improve fuel efficiency, N
There is a need to be able to reduce and remove Ox, and the emergence of a catalyst that can perform denitrification over a wide range of 02 concentrations has been awaited.

In recent years, it has been reported that a catalyst obtained by ion-exchanging Cu with silica gel or zeolite is effective for the direct decomposition of NO (e.g., Japanese Patent Laid-Open No. 125250/1983). When used as a purification catalyst, [:0. The combustion of HC is remarkable, and the combustion of N
There were problems in that the reduction and removal of Ox did not proceed very well and furthermore, the heat resistance was poor.

[A means of promise to solve problems]

The present invention aims to solve the above-mentioned problems of the prior art, and provides a catalyst in which copper and a specific active metal are combined using crystalline silicate having a specific composition and crystal structure. The inventors have discovered that NOX, Co, and H[: can be reduced even in the vicinity of the stoichiometric air-fuel ratio and in the region higher than the stoichiometric air-fuel ratio, that is, in a state where a large amount of oxygen exists, and have completed the present invention.

That is, the present invention (1) has the X-ray diffraction characteristics shown in Table A below, and in the dehydrated state, expressed as the molar ratio of the oxide, (1,0±0.8)R2[+- [aM, 03-b^12
L]・ysto.

(However, in the above formula, R is an alkali metal ion and/or hydrogen, M is an ion of one or more elements selected from the group consisting of group II metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium. , a+b=1.a≧0
゜b≧0. An exhaust gas treatment catalyst made by coexisting copper and a specific metal in a crystalline silicate having a chemical formula of y>11).

Table A [Irradiation is copper Kc X-ray] [Io is the strongest peak intensity, I/1. is the relative strength] (2) The active metals listed above are magnesium, calcium, barium, strontium, lithium, sodium, potassium, boron, aluminum, phosphorus, tin, antimony, silicon, titanium, zinc, vanadium, niobium, iron, and cobalt. , nickel, manganese, lanthanum,
Cerium, praseodymium, neodymium, samarium,
The exhaust gas treatment catalyst according to (1) above, which contains at least one type of tungsten.

It is.

[Action] Regarding the action of the catalyst used in the present invention, the redox cycle of ion-exchanged copper ions (Cu"-"Cu")
The copper on the crystalline silicate activates CD and HC, and these activated gases react with No to remove NOx. Furthermore, by coexisting copper with other metals, the heat resistance of the active metal (copper) was improved, making it possible to improve the selectivity of the denitrification reaction.

In other words, the above metals have the effect of suppressing the sintering of Cu at high temperatures while maintaining the NO adsorption capacity and redox cycle capacity of Cu ions, and include magnesium (Mg), calcium (Ca), barium (Ba), etc. )
Strontium (Sr) Lithium (Li) Sodium (Na) Potassium (K), Boron (B),
Aluminum (AI), phosphorus (P), tin (3 ports)
Antimony (Sb) Silicon (Si) Titanium (
Ti), zinc (Zn), vanadium (v), niobium (Nb), iron (pe): lbalt (CO), nickel (Ni), manganese (Mn), lanthanum (La)
, cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sn+), and tungsten (11).

These metals can be supported on a crystalline silicate having a specific crystal structure and a specific composition by an ion exchange method, and can be made to coexist with copper. Furthermore, various salts such as nitrates, chlorides, and sulfates can also be supported on the above-mentioned carrier by an impregnation method.

The preferred content of copper and other metals supported on the specific crystalline silicate carrier used in the present invention is carrier 1
0.00 parts by weight, Cu is 0.2 to 30 parts by weight, preferably 0.4 to 20 parts by weight, while other metals include Mg,
Ca, Ba, Sr, Li.

Na, K, B, AI, P, Si, S
n is 0.2 to 8 parts by weight, Sb, Ti, Zn, V
, Nb, Fe, Co, Ni, Mn, La,
Ce.

Pr, Nd, Sm, - are 0.1 to 6 parts by weight.

The crystalline silicate used in the present invention includes a source of silica, a group III element, a rare earth element, titanium, vanadium,
forming a reaction mixture containing a source of oxides of chromium, niobium, antimony, and gallium, a source of alumina, a source of alkali, water, and an organic nitrogen-containing compound; It is synthesized by heating.

Furthermore, the crystalline silicate used in the present invention is 5102
/ High silica zeolite with an Al2O3 ratio of 12 or more or a part of A1 in the structure of conventional zeolite is a group element, a rare earth element, titanium, vanadium, chromium, niobium,
It replaces antimony and chromium, and is characterized by a 5102/(M-03+A12O3) ratio of 12 or more, and is produced from a reaction mixture having the following molar composition.

5102/ (M2O3+^12O-) 12~3
000 (preferably 2O to 2O0) DH”' /Si0.0 to 1.0 (preferably 0.2 to 0.8) H2O/5in22 to 1000 (preferably 10 to 2O0) Organic nitrogen-containing compound/( LOs +A12O3) (preferably 5 to 50) For industrial use of the catalyst used in the present invention, it is desirable to use it after forming it into an appropriate shape.For example, inorganic oxides such as silica, alumina, or clay is used as a binder, and if necessary, a forming aid such as an organic substance is used to form it into a spherical, columnar, or honeycomb shape.The crystalline silicate before supporting copper and other metals is formed in advance, and the formed body is injected with copper ions. The catalyst replaced with the above can also be considered as the catalyst used in the present invention.The size of the molded body is not particularly limited.

[Example 1] Crystalline silicate was synthesized as follows.

Water glass, ferric sulfate, aluminum sulfate, water to Na2O' (0,lFe2Oa ” 0.9A12O
3) "30S102・1600)+2O molar ratio, add an appropriate amount of sulfuric acid to adjust the pH of the mixture to around 9, and add propylamine and odor as organic nitrogen-containing compounds. pe2O
a + ^12O. 20 times the total number of moles was added, mixed well, and placed in a 500 CO stainless steel autoclave.

The above mixture was heated to 160 ml while stirring at about 50 Orpm.
The reaction was carried out at ℃ for 3 days. After cooling, the solid content was filtered, thoroughly washed with water until the pH of the washing water became approximately 8, and heated at 110°C for 12 hours.
It was dried for an hour and fired at 550°C for 3 hours.

The crystal grain size of this product is around 1μ, and the composition expressed in molar ratio of oxides is expressed in dehydrated form (H,N
a) 2O” (0,IFe,O,+0.9A1.
D3) It was '30S102. This is called crystalline silicate 1.

When synthesizing this crystalline silicate 1, it is possible to use hydrochloric acid instead of sulfuric acid among the raw materials, ferric chloride instead of ferric sulfate, or silica sol instead of water glass. A similar silicate was obtained using

Furthermore, similar silicates were obtained by reacting at 170°C or 180°C for 2 days instead of at 160°C for 3 days as the hydrothermal synthesis conditions.

Repeat the same operations as for crystalline silicate 1, except that the amounts of ferric sulfate and aluminum sulfate added when preparing the raw materials for crystalline silicate 1 were converted into the molar ratio of FezO3 and Al2O3 and changed as shown below. crystalline silicate 2
~4 was adjusted.

When preparing crystalline silicate 1, hydrochloric acid was used instead of sulfuric acid, and cobalt chloride, ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride,
Antimony chloride and gallium chloride are each converted into oxides of Pe.
Crystalline silicates 5 to 14 were prepared by repeating the same operation as for crystalline silicate 1 except that the same number of moles as 2Oa was added. The composition of these crystalline silicates excluding organic nitrogen-containing compounds is the molar ratio of oxides (dehydrated form)
Expressed as (H,Na)2O'' (0,1M2O3
0.9A12O3)" 30Si02Te.Here, M is Co, Ru, Rh, La, Ce, Ti
, V.

[:r, Sb, Ga (crystalline silicate 5-14
(in numerical order).

In addition, in crystalline silicate 1, 5I02/
(0,1Fe2O3 + 0.9A12O3) ratio 2O
．． Crystalline silicates 15 and 16 were prepared by repeating the same operation as for crystalline silicate 1, except that the silicates were changed to 80%.

It was confirmed that the powder X* diffraction patterns of the above crystalline silicates 1 to 16 showed the patterns shown in Table 1.

10 g of each of the above crystalline silicates 1 to 16 was placed in an aqueous solution in which 1 g of cupric chloride and 1 g of zinc chloride were dissolved in 500 cc of water, and an ion exchange operation was performed by stirring at room temperature for 12 hours. After repeating this ion exchange operation three times, it was washed with water and dried at 100°C for 12 hours.
16 (corresponding to the number of crystalline silicate) was prepared.

Furthermore, 10 g of crystalline silica) 1 was added to cupric chloride (C
uCl2 ・2H2O) 1 g and zinc chloride (ZnC
1z), calcium chloride (Cat: I2.H,
O), barium chloride (BaC12.2H,0), strontium chloride (SrC12.6H2O), sodium chloride (NaC1) potassium chloride (KCI), boric acid (8
3BO,), aluminum chloride (AIC1,), tin chloride (SnC12・2H2O) silicon tetrachloride (SIC1
An ion exchange operation was performed in which 1 g of each of 4) was dissolved in 500 cc of water and stirred for 12 hours at room temperature. After repeating this ion exchange operation three times, wash with water,
Catalysts 17 to 25 were prepared by drying at 100°C for 12 hours.

In addition, cupric chloride (Cu
[:lz ・2H2O) and antimony chloride (5bC1
s), titanium tetrachloride (TIC14), vanadium trichloride (vC13), niobium chloride (NbCIS), iron trichloride (
Cobalt chloride ([:0CI2 ・6LO
), nickel chloride (NIC12.6H2O), manganese chloride (MnC12-482O), lanthanum chloride (La
Aqueous solutions of cerium chloride (Ce[:I3), praseodymium chloride (PrC1+ .7H2O), neodymium chloride (NdC13), samarium chloride (SmCI+), and tungsten chloride (WCl2) were added to the crystalline silicate. Cu 0.6 mmo in atomic ratio
1/g, the above elements were impregnated so as to support Q, 4 mmol, and dried at 110°C for 24 hours.
No. 39 was prepared.

Catalysts 1 to 39 were sized into 16 to 32 meshes, and catalysts 0.
5 g was packed into an atmospheric fixed bed flow reactor and an activity evaluation test was conducted under the following reaction conditions. The results are also shown in Table 2.

Gas composition: NO: 500ppm, C3H6: 5
00ppm, CO: 0.5%, 0.00ppm. :2%, He
Balance gas flow rate: 2Nlh, reaction temperature: 500℃
[Comparative Example 1] 10 g of crystalline silicate 1 described in Example 1 was added to an aqueous solution in which 1 g of cupric chloride was dissolved in 500 cc of water, and an ion exchange operation was performed by repeating stirring three times for 12 hours at room temperature. Ta. After ion exchange, it was washed with water and dried at 100° C. for 12 hours to prepare catalyst 40.

An activity evaluation test was conducted on this catalyst 40 under the same conditions as those shown in Example 1. The results are also shown in Table 2.

[Example 2] 0.5 g of Catalyst 1 of Example 1 and Catalyst 40 of Comparative Example 1 were packed into an atmospheric pressure fixed bed flow reactor, and an activity evaluation test was conducted under different reaction conditions. The results are shown in Table 3.

In addition, the activity evaluation result after 100 hours shown in Table 3 is 73
These are the results of an activity evaluation conducted after a forced heating test at 0° C. for 100 hours (gas composition atmosphere).

As described above, it was found that the catalyst used in the present invention has high activity even when using a gas containing SO3, and that the activity changes little over time.

[Example 3] A mixture of ferric chloride and chromium chloride was used instead of ferric sulfate when preparing the raw material for crystalline silicate 1 in Example 1,
NazO・(0.09Fez03・0.01Cr2L
・0.9^1.0. )-30Si02-1600H,
Crystalline silicate was obtained in the same manner as Crystalline Silicate 1, except that the molar ratio was adjusted to 0, and Catalyst 41 was obtained by co-ion exchange of Cu and Zn in the same manner.

In addition, co-ion exchange of three metals, Cu, 2n, and Mg, was carried out using crystalline silicate 1 in the same manner as in Example 1,
A catalyst 42 was obtained. Table 2 also shows the results of the same activity evaluation as in Example 1.

〔Effect of the invention〕

As shown in the examples above, in the present invention, by using a catalyst in which copper and a specific metal are combined with a crystalline silicate having a specific crystal structure and a specific composition,
NO in exhaust gas containing NOx, Co, and HC
It becomes possible to reduce X, CO, and HC.

In this example, the activity evaluation test was carried out using the present catalyst in the form of granules, but it is possible that the present catalyst would have an effective effect even in the form of a honeycomb substrate such as cordeurite. Needless to say.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the composition of automobile exhaust gas (without catalyst), and FIG. 2 is a diagram of the composition of exhaust gas when a three-way catalyst is used.

Claims (2)

[Claims] (1) It has the X-ray diffraction characteristics shown in Table A below, expressed as the molar ratio of oxide in a dehydrated state, (1.0±0.8)R_2O・[aM_2O_3・bA
l_2O_3]・ySiO_2 (However, in the above formula, R is an alkali metal ion and/or hydrogen, M is a group VIII metal,
One or more element ions selected from the group consisting of rare earth metals, titanium, vanadium, chromium, niobium, antimony, and gallium, crystalline with the chemical formula a+b=1, a≧0, b≧0, y>11) An exhaust gas treatment catalyst characterized by being made by coexisting silicate with copper and a specific metal. Table A ▲ Contains mathematical formulas, chemical formulas, tables, etc. ▼ W: Weak M: Intermediate S: Strong VS: Very strong [Irradiation is copper Kα ray] [I_0 is the strongest peak intensity and I/I_0 is relative intensity] (2) The other active metals mentioned above are magnesium, calcium,
Barium, strontium, lithium, sodium, potassium, boron, aluminum, phosphorus, tin, antimony, silicon, titanium, zinc, vanadium, niobium, iron, cobalt, nickel, manganese, lanthanum, cerium, praseodymium, neodymium, samarium, tungsten. The exhaust gas treatment catalyst according to claim 1, which contains at least one kind selected from among them.