JP2557712B2 - Exhaust gas purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used in an oxygen atmosphere where the air-fuel ratio is on the lean side (A / F> 14.7) and is used under the use condition where heat resistance is required.
The present invention relates to an exhaust gas purification method capable of efficiently purifying NO _x .

(Prior Art) In an internal combustion engine such as an automobile, low fuel consumption is required from the viewpoint of energy saving. As one of the means for reducing fuel consumption, it has been conventionally practiced to burn an oxygen-rich mixture during traveling. However, in such an oxygen-rich atmosphere where the air-fuel ratio is lean, even though HC and CO of harmful components in the exhaust gas can be removed by oxidation, NO _x contacts with the catalyst metal by O ₂ adsorbed on the catalyst bed. However, even if the catalyst metal can be contacted and reduced, even if it can be reduced, nitrogen immediately binds to oxygen adsorbed on the catalyst bed, so that the purification efficiency becomes extremely low. there were. In order to solve such problems, USP
4297328 is Cu in the many pores on the surface of zeolite.
We have developed a catalyst that supports and put it in an oxidizing atmosphere to reduce and remove NO _x . However, the catalyst using this zeolite is inferior in heat resistance and durability and has a problem in practical use.

Therefore, the inventors of the present invention have diligently studied to solve the above problems, and as a result of repeating various systematic experiments, it has been conventionally used when a crystalline silicoaluminophosphate porous material is used as a catalyst having an active element supported thereon. The present invention has been completed by finding that NO _x can be efficiently purified under use conditions requiring higher heat resistance than the purification method using zeolite.

(Object of the Invention) It is an object of the present invention to provide an exhaust gas purification method capable of efficiently purifying NO _x under use conditions requiring heat resistance in an oxygen-rich atmosphere with a lean air-fuel ratio.

(Explanation of the First Invention) The first invention (the invention according to claim (1)) is an exhaust gas purification method for removing NO _{x in} exhaust gas in an oxidizing atmosphere. And a catalyst in which at least one active element of alkaline earth metal is supported on a crystalline silicoaluminophosphate porous carrier, the catalyst is contacted with an exhaust gas containing nitrogen oxide, hydrocarbon and oxygen, Catalytic purification of nitrogen oxides and hydrocarbons from exhaust gas by selective reaction in an oxidizing atmosphere between nitrogen oxides adsorbed on active elements and hydrocarbons present in the exhaust gas. Exhaust gas purification method.

The crystalline silicoaluminophosphate used as a carrier in the first aspect of the present invention has a large number of pores on its surface, its diameter is 5 to 10Å, which is slightly larger than the size of NO _x molecule. A transition metal or the like, which is an active element that reduces NO _x , is supported on the surface of the silicoaluminophosphate and the surface inside the pores. Since the supported amount is extremely large inside the pores, the reduction reaction of NO _x is mainly
NO _x is selectively adsorbed on active sites such as Cu in the pores. Also, the catalyst used in the present first invention is to selectively promote HC-NO _x reaction by solid acidic crystalline silicoaluminophosphate phosphate.

Since the exhaust gas purification method of the first aspect of the invention utilizes such an action, NO _x can be efficiently purified even in an oxygen excess atmosphere where the air-fuel ratio is on the lean side. That is, since NO _x is selectively adsorbed on Cu or the like in the pores, contact with the active site such as Cu is not obstructed by O ₂ , and NO _x can be reduced and removed even in an oxidizing atmosphere.

Further, the catalyst used in the exhaust gas purifying method according to the first aspect of the present invention does not collapse the skeletal structure of silicoaluminophosphate, which is the carrier constituting the catalyst, even at 900 to 1000 ° C., and therefore the pores present on the surface thereof It does not disappear or shrinks, and it has excellent heat resistance and durability, and can be used under operating conditions that require heat resistance.

(Explanation of Second Invention) Hereinafter, an invention (hereinafter referred to as a second invention) which embodies the first invention will be described.

The active element used by being supported on crystalline silicoaluminophosphate means Cu, Fe and alkaline earth metals Ca, Mg, Ba which have the ability to reduce NO _x . Of these, Cu
Is most desirable.

The crystalline silicoaluminophosphate that is a carrier has uniform pores, a nominal diameter larger than about 3Å, is anhydrous, and has a chemical composition of the general formula (Si _x Al _y P _z ) O ₂ (x + y + z = 1,0.01 ≦ x <0.8, z ≧ 0.01) is used.

The pore diameter is preferably about 5 to 10 Å, which is slightly larger than the NO _x molecular diameter. The proportion of Si in the silicoaluminophosphate is in the range of 0.01 ≦ x <0.8, preferably 0.0
5 to 0.25 is good. When it is less than 0.05, the solid acidity is weakened, the ability to carry active elements, especially the ion exchange ability is lowered, and the catalytic activity becomes insufficient. When it is 0.25 or more, the heat resistance decreases, which is not preferable. The amount of the active element supported is preferably 0.5 to 6 wt% with respect to the crystalline silicoaluminophosphate.
If it is less than 0.5 wt%, the ability to reduce NO _x is low, and 6w
There is no increase in the reduction capacity even if it exceeds t%.

The catalyst used in the second invention is produced as follows. The silicoaluminophosphate may be synthesized by a commonly used method, for example, phosphate, hydrated alumina and silica sol are used as starting materials, these are uniformly mixed, and an organic substance is added to the mixture to define the pore structure. After mixing and stirring so as to be uniform, a crystalline silicoaluminophosphate powder is obtained by hydrothermal synthesis.

Examples of the organic substance include quaternary ammonium, quaternary amine, tetrapropylammonium ion, tetraethylammonium ion, tripropylamine, triethylamine, triethanolamine, piperidine, cyclohexylamine, 2-methylpyridine, N, N-dimethylbenzylamine. , N, N-diethylethanolamine, dicyclohexylamine, N, N-dimethylethanolamine, choline, N, N-dimethylpiperazine, 1,4-diazobicyclo- (2,2,2) octane, N-methyldiethanolamine, N-methylethanolamine, N-methylpiperidine, 3-methylpiperidine, N-methylcyclohexylamine, 3-methylpyridine, 4-methylpyridine, quinuclidine, N, N-dimethyl-1,4-diazabicyclo- (2,2 , 2) Octane ion, Tetramethy Ruammonium ion, tetrabutylammonium ion, tetrapentylammonium ion, di-n-butylamine,
Neopentylamine, di-n-pentylamine, isopropylamine, i-butylamine, ethylenediamine and 2-imidazolidone, di-n-propylamine and polymeric quaternary ammonium salt [(C ₁₄ H ₂₃ N ₂ ) ²⁺ ] _x [where x has at least two values] is used.

Next, the powder is loaded with an active element. The active element is supported by immersing the silicoaluminophosphate powder in an aqueous solution of the salt of the active element for 1 to 2 hours and then drying it in the air.
Alternatively, by an ion exchange method comprising a step of immersing the silicoaluminophosphate powder in an aqueous solution of the salt for one day and then washing with water for 1 to several times, and then holding it at a temperature of 500 to 700 ° C. for several hours and baking it. To do. The supporting force by the ion exchange method is stronger than that of the active element.
The powdery catalyst thus obtained may be used as it is, or a binder such as alumina sol or silica sol may be added to the catalyst powder to form a desired shape, or water may be added to form a slurry, such as a honeycomb. In the form of Al ₂ O ₃
It is used by coating it on a refractory substrate such as.

(Example) Hereinafter, the Example of this invention is described.

That is, in an oxidizing atmosphere using a catalyst in which an active metal is supported on a crystalline silicoaluminophosphate porous carrier,
The effectiveness of the exhaust gas purification method according to the present invention was confirmed by bringing the catalyst into contact with exhaust gas containing NO _x and hydrocarbons.

Example 1 A catalyst used in the exhaust gas purification method of this example was adjusted,
The catalyst was heat-treated in a lean model gas atmosphere with excess oxygen, and then the NO _x purification rate was measured to evaluate the purification activity. Further, the same activity evaluation was performed for the comparative catalyst.

Preparation of catalysts of this example (No. 1 to No. 7); First, crystalline silicoaluminophosphate was synthesized.

Mixing 85 wt% of ortho phosphoric acid (H ₃ PO ₄₎ and 26.0g of water 10.4 g, this hydrated oxide of aluminum pseudoboehmite phase
6.0 g was added and stirred until homogeneous. To the mixture, 3.0 g of colloidal silica (SiO ₂ 20 wt%) was added and mixed until homogeneous, and further 8.4 ml of triethylamine as an organic substance was added to the mixture and stirred until homogeneous. Next, the mixture was sealed in a pressure vessel made of stainless steel lined with polytetrafluoroethylene, heated at 180 ° C. for 72 hours, then the reaction mixture was taken out from the pressure vessel, and only the solid reaction product was collected by filtration. Washed with water and dried. Further, the product is calcined at 600 ° C. for 1 hour to decompose and remove organic matter to obtain a crystalline silicoaluminophosphate having a composition ratio of (Si _0.05 Al _0.50 P _0.45 ) O ₂ and a pore size of about 8Å. It was

Subsequently, the crystalline silicoaluminophosphate was added to 0.1M.
It was immersed in an aqueous solution of copper acetate for 24 hours, filtered and washed, and then calcined at 600 ° C. for 2 hours to obtain a crystalline silicoaluminophosphate catalyst No. 1 carrying Cu as an active element by an ion exchange method. . The amount of Cu supported is about 2.5 wt in terms of CuO.
%Met.

Further, a crystalline silicoaluminophosphate having a pore size of about 7Å was obtained under the same conditions as the catalyst No. 1 except that an aqueous solution of tetrapropylammonium hydroxide was used instead of the n-triethylamine, and the catalyst No. 1 was used. Under the same conditions, a crystalline silicoaluminophosphate catalyst No. 2 supporting about 2.5 wt% of Cu in terms of CuO was obtained.

Also, under the same conditions as the above catalyst No. 1 except that di-n-propylamine was used instead of n-triethylamine, crystalline silicon having a pore size of about 6Å carrying about 2.5 wt% of Cu in terms of CuO. Aluminophosphate catalyst No. 3 was obtained.

The catalyst No. 1 except that the amount of colloidal silica was changed from 3.0 g to 6.0 g and the amount of orthophosphoric acid was changed from 10.4 g to 9.2 g.
Under the same conditions as above, the composition ratio supporting Cu (Si _0.1 Al _0.5 P
_0.4 ) O ₂ crystalline silicoaluminophosphate catalyst No. 4
I got The composition ratio carrying about 2.5 wt% of Cu in terms of CuO in place the amount of orthophosphoric acid in 5.8g in 15g amounts of colloidal silica as well (Si _0.25 Al _0.5 P _0.25) crystalline O ₂ silico aluminophosphates Catalyst No. 5 was obtained.

In addition, a Ca-supporting crystalline silicoaluminophosphate catalyst No. 6 was obtained under the conditions of the above-mentioned catalyst No. 1 except that calcium acetate was used instead of copper acetate to support Ca as an active element. The loading amount of Ca was 1.6 wt%.

In addition, 4.5 wt% Cu in terms of CuO was obtained by a Cu loading method in which it was immersed in a crystalline silicoaluminophosphate 1M copper acetate aqueous solution produced with the above catalyst No. 1 for 2 hours and dried in the air.
-Supported crystalline silicoaluminophosphate catalyst N
I got o.7.

Then mixed with water 85 wt% of H ₃ PO ₄ and 20.4g of aluminum isopropoxide and 40g of 11.6 g, were mixed to homogeneity, further added tetraethylammonium hydroxide aqueous solution to the mixture After stirring until homogeneous, catalyst No. 1 was used except that the heating temperature in the pressure vessel was set to about 200 ° C.
Under the same conditions as above, a crystalline silicoaluminophosphate catalyst No. 8 having a composition ratio of (Si _0.12 Al _0.4 P _0.48 ) O ₂ with a Cu content of about 2.5 wt% and a pore size of about 4.3 Å was obtained. .

Further, the composition ratio supporting about 2.5 wt% Cu content in terms of CuO (Si _0.15 Al) under the same conditions as catalyst No. 8 except that di-n-propylamine was used instead of the tetraethylammonium hydroxide aqueous solution. _A crystalline silicoaluminophosphate catalyst No. 9 having _0.39 P _0.46 ) O ₂ and a pore size of about 6Å was obtained.

Preparation of comparative catalyst (No.C1): Zeolite with Si / Al ratio of 40 was immersed in 0.1M copper acetate aqueous solution for 24 hours, and then the mixture was filtered and washed, and further 600 ° C
The zeolite catalyst No. C1 supporting Cu was obtained by the ion exchange method of calcination for 2 hours. The amount of Cu supported is 3 wt in terms of CuO
%Met.

Heat resistance / durability test The powders of the catalyst Nos. 1 to 9 of the present example and the catalyst No. C1 of the comparative example were subjected to 500, 600, 500, 600 Heat treatment was carried out at 700 and 800 ° C. for 5 hours each. The composition of this model gas is 0.47% CO,
8.4% O ₂ , 0.16% H ₂ , 9.0% CO ₂ , 0.1% C ₃ H ₆ (THC3000pp
m) and 1000 ppm NO.

Purification activity evaluation The NO purification rate at room temperature to 600 ° C was measured using the catalysts tested as described above.

At the time of measurement, a powdery catalyst was pressure-molded into pellets of about 2 mmφ, which were filled in an experimental catalytic converter, and an exhaust model gas in an oxidizing atmosphere was introduced. The composition of the gas is 0.
10% CO, 4.0% O ₂ , 0.03% H ₂ , 0.04% C ₃ H ₆ (THC0.12
%), 10.0% CO ₂ , 670 ppm NO, and space velocity G at measurement
HSV was about 30,000 / hour. Each in Table 1 The maximum purification rate of the catalyst at each temperature is shown. The catalyst of the present example has excellent heat resistance and durability as compared with the comparative catalyst, and the exhaust gas purification method according to this example can be used under the use condition where heat resistance is required.

Example 2 The results of evaluating the heat resistance and durability of the catalyst according to this example in consideration of driving in urban areas will be described below.

Preparation of catalyst No. 10 of this example: The catalyst No. 1 of Example 1 was molded into a powder having an average particle size of 5 μm with a ball mill. 100 parts by weight of the powder, 20 parts by weight of silica sol (solid content 10%) and 50 parts of water were mixed and stirred to give a viscosity of 200
A ~ 300 cps slurry was prepared. Next, a commercially available honeycomb base material (volume 1.7, cell number 400, cordierite quality) was prepared, the surface thereof was coated with the slurry, the excess was blown off with an air stream, dried and fired. Catalyst No. 10 thus obtained contains 140 g of Cu-supported crystalline silicoaluminophosphate per 1 carrier.

Preparation of comparative catalyst No. C2: Comparative catalyst No. C2 was obtained from comparative catalyst No. C1 under the same conditions as in the case of preparing catalyst No. 10.

Purification activity evaluation This catalyst No. 10 and comparative catalyst No. C2 were attached to a converter, the converter was attached to a lean burn engine exhaust system with a displacement of 1.6, and a durability test was conducted in a pattern simulating urban driving, and every 200 hours. The NO _x purification rate was measured. The average air-fuel ratio of the engine is 22 with lean oxygen, the maximum temperature is 750 ° C, and the test time is 600 hours. The results obtained are shown in Table 2.

The catalyst No. 10 of the present example shows remarkable durability especially after 200 hours or more as compared with the comparative catalyst even under conditions close to urban driving, and practical NO _x even after 600 hours.
The purification performance is maintained, and the exhaust gas purification method of this embodiment using the catalyst No. 10 of the embodiment can be used under the use condition where heat resistance is required.

Claims (1)

(57) [Claims] 1. A catalyst in which at least one active element of Cu, Fe and an alkaline earth metal is supported on a crystalline silicoaluminophosphate porous carrier is prepared, and the catalyst is mixed with nitrogen oxide, hydrocarbon and oxygen. Contact with exhaust gas containing
Catalytic purification of nitrogen oxides and hydrocarbons from exhaust gas by a selective reaction in an oxidizing atmosphere between nitrogen oxides adsorbed on the active element and hydrocarbons present in the exhaust gas. Exhaust gas purification method.