JPH09164335A - Exhaust gas-purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mixed catalyst excellent in NOX purifying ability under a steam atmosphere by mixing a zeolite with an alumina catalyst, a silica catalyst or an alumina multiple catalyst to form an exhaust gas purifying catalyst. SOLUTION: This exhaust gas-purifying catalyst is prepared by mixing zeolite with the alumina catalyst, the silica catalyst or the alumina multiple catalyst and the particle diameter of zeolite to be mixed and at least one of the alumina catalyst, the silica catalyst or the alumina multiple catalyst is controlled to <=1mm. An alumina carrying a transition metal as the alumina catalyst, a silica carrying a transition metal as the silica catalyst and an alumina multiple oxide containing at least one kind of a transition metal and Al as the alumina multiple catalyst are used. The content of the transition metal in the alumina catalyst or the alumina multiple catalyst is controlled to >=15% to <=45% and the quantity of zeolite to be mixed is controlled to >=5% but <=95%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst composed of a mixed catalyst having a particularly high heat resistance and an excellent NO _x (nitrogen oxide) purifying ability.

[0002]

The NO _X purification catalyst in an oxygen excess atmosphere such as Related Art Diesel and lean-burn engine exhaust, ion-exchange zeolite catalysts, although active metal supported catalysts is known, yet the level of practical use There is nothing that has reached.

The conventionally synthesized active metal-supported catalyst is prepared by supporting the active metal on a carrier such as alumina, and the ion-exchanged zeolite catalyst is prepared by carrying out ion-exchange of the active metal with zeolite. It is usually done.

[0004]

However, the ion-exchanged zeolite catalyst is put to practical use in an atmosphere of water vapor in which active metal ions move or dealumination occurs at the ion-exchange site to cause irreversible deterioration in catalytic activity. It is difficult. Further, the active metal-supported catalyst does not undergo irreversible deterioration in a steam atmosphere, but there is a problem in that the purifying ability is hindered by steam.

The present invention has been made to solve such conventional problems, and an object of the present invention is to provide a mixed catalyst having an excellent NO _x purification ability especially in a steam atmosphere.

Another object of the present invention is to provide a mixed catalyst having high heat resistance by using zeolite which has not been subjected to ion exchange without causing irreversible deterioration of catalytic activity in a steam atmosphere. And

Zeolite that has not been subjected to ion exchange as referred to herein has no NO _x purification ability, but has the ability to activate hydrocarbons. The activated hydrocarbons to act as an effective reducing agent to the selective reduction of the NO _X in an oxygen-rich atmosphere is known.

In the present invention, the zeolite not subjected to such ion exchange is treated with an alumina catalyst, a silica catalyst,
Alternatively, by physically mixing with the alumina composite catalyst,
It is intended to improve the NO _X purification capacity.

At this time, the materials to be physically mixed must have a certain particle size or less. This is because there is a limit to the feasible distance of activated hydrocarbons and the material is too far, due to the fact that not happen enough _the NO _X selective reducing reaction.

[0010]

The exhaust gas purifying catalyst provided by the present invention is one described in the following (1) to (6).

(1) An exhaust gas purification catalyst prepared by mixing zeolite with an alumina catalyst, a silica catalyst, or an alumina composite catalyst.

(2) The exhaust gas purifying catalyst according to (1) above, wherein the particle size of at least one of the zeolite and the alumina catalyst, the silica catalyst, or the alumina composite catalyst mixed in the catalyst is 1 mm or less.

(3) The exhaust gas purifying catalyst according to the above (1), wherein alumina carrying a transition metal is used as the alumina catalyst in the catalyst.

(4) The exhaust gas purifying catalyst according to the above (1), wherein silica supporting a transition metal is used as the silica catalyst in the catalyst.

(5) The exhaust gas purifying catalyst according to (1) above, which uses an alumina composite oxide containing at least one transition metal and Al as the alumina composite catalyst in the catalyst.

(6) The exhaust gas purifying catalyst according to (1) above, wherein the content of transition metal in the alumina catalyst or the alumina composite catalyst in the catalyst is 15% or more and 45% or less.

(7) The exhaust gas purifying catalyst according to (1) above, wherein the amount of zeolite mixed in the catalyst is 5 wt% or more and 95 wt% or less.

[0018]

In the exhaust gas purifying catalyst of the present invention, the zeolite is NO of alumina catalyst, silica catalyst, or alumina composite catalyst.
Since it has a function of complementing the _X purification capacity, the NO _X purification capacity is improved especially in a steam atmosphere.

Further, the exhaust gas purifying catalyst of the present invention does not irreversibly deteriorate the catalytic activity in a steam atmosphere. This is because in the case of ion-exchanged zeolite that has undergone ion exchange of active metals, the dealumination is promoted at the ion-exchange sites due to the presence of active metal ions at the ion-exchange sites, and zeolite crystal collapse occurs. This is because, in the case of zeolite that has not been ion-exchanged, dealumination is not promoted, and thus zeolite crystals are less likely to collapse even in a steam atmosphere.

Generally, in the case of ZSM-5 zeolite,
Originally, it has a heat resistance of 1000 ° C. But, for example,
It is known that the heat-resistant temperature is lowered to 500 ° C. by ion exchange with copper. In the present invention, since zeolite that has not undergone ion exchange is used, it has high thermal durability even in a steam atmosphere.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) (1) Synthesis of mixed catalyst obtained by mixing zeolite and alumina composite catalyst An aqueous solution was prepared by mixing aluminum nitrate and copper nitrate such that Cu was 1 to 50 wt% in terms of oxide. While stirring this aqueous solution, ammonia water diluted to 0.5 to 3% was slowly added dropwise to this to neutralize Cu and A.
l of coprecipitate was obtained. This coprecipitate is filtered and washed with pure water to remove C
A u-Al gel was obtained. After air-drying it, it was dried at 110 ° C overnight and ground in a mortar to obtain a powder, which was then dried at 700 ° C for 1 hour.
It was calcined for an hour to synthesize an alumina composite catalyst (CuAlO).

Zeolite (Na-type ZSM-5) not subjected to ion exchange with this alumina composite catalyst (SiO ₂ /
Al2O3 = 23.8) was mixed in a mortar so that the weight ratio was 50:50 and mixed catalyst (CuAlO / NaZS
M5) was obtained.

(2) Performance test of mixed catalyst The NO _X purification activity was measured by a fixed bed atmospheric pressure flow reactor. The composition of the reaction gas is NO: 1000 ppm, C
₃ H ₆ : 1000 ppm, CO: 1200 ppm, H
₂ : 400 ppm, O ₂ : 6%, CO ₂ : 10%, H _{2
O: 10%, N 2:} Bal. And GHSV (space velocity)
Was performed at 200,000 h ^-1 . At this time, N ₂
No O formation was observed.

Table 1 and FIG. 1 and Table 2 and FIG. 2 show the test results. 1 shows the data of Table 1 and FIG. 2 shows the data of Table 2 in the form of a graph.

[0025]

[Table 1]

[0026]

[Table 2]

(3) Performance evaluation of mixed catalyst When the Cu content of the alumina composite catalyst is 15 wt% (oxide conversion) or more, the mixing effect appears. This seems to be related to the ratio of the alumina portion and the metal portion on the surface of the alumina composite catalyst. NO _x near 25 wt%
It can be seen that the selective reduction of is promoted most. Also, 25
It can be seen that water is not affected near%.

Other transition metals (Japanese Patent Application No. 7-6612)
(See No. 5) or a composite oxide catalyst containing silica, the same mixing effect can be obtained.

(Embodiment 2) (1) Synthesis of mixed catalyst prepared by mixing zeolite and alumina catalyst γA12O3 was prepared by preparing Cu-free Al oxide. On the other hand, an aqueous solution was prepared by mixing this γAl ₂ O ₃ with copper nitrate such that CuO was 1 to 50 wt% in terms of oxide. Then, in this aqueous solution, γA1
2O3 was added, and while stirring the aqueous solution containing γA12O3, ammonia water diluted to 0.5% to 3% was slowly added dropwise to the solution to neutralize it so that Cu was supported on γA12O3 (alumina catalyst (CuO- γAP) was prepared.

Zeolite (Na type ZSM-5) (SiO2 / A1) which has not been ion-exchanged with this alumina catalyst
2O3 = 23.8) was mixed in a mortar so that the weight ratio was 50:50, and the mixed catalyst (CuO-γAP / NaZS) was mixed.
M5) was obtained.

(2) Performance test of mixed catalyst The NO _X purification activity was measured by a fixed bed atmospheric pressure type reaction apparatus. The composition of the reaction gas is NO: 1000 ppm, C ₃
H ₆ : 1000 ppm, CO: 1200 ppm, H ₂ :
400 ppm, O ₂ : 6%, CO ₂ : 10%, H ₂ O:
10%, N ₂ : Bal. And GHSV (space velocity) is 2
It was carried out at 0,000 h ^-1 . At this time, generation of N ₂ O was not recognized.

Table 3 and FIG. 3 and Table 4 and FIG. 4 show the test results. 3 is a graph showing the data of Table 3 and FIG. 4 is a graph showing the data of Table 4.

[0033]

[Table 3]

[0034]

[Table 4]

(3) Performance Evaluation of Mixed Catalyst As is apparent from the test results, it is found that the same mixing effect as that of the first embodiment is obtained.

(Embodiment 3) (1) Synthesis of mixed catalyst obtained by mixing zeolite and hydrothermally treated alumina composite catalyst An aqueous solution was prepared by mixing aluminum nitrate and copper nitrate so that Cu was 5 wt% in terms of oxide. . While stirring this aqueous solution, ammonia water diluted to 0.5 to 3% was slowly added dropwise to the solution for neutralization to obtain a coprecipitate of Cu and Al. At this time, if the solution concentration is too high or the ammonia water dropping rate is too fast, a uniform mixture at the atomic level cannot be obtained. The solution concentration must be 0.4 mol / l or less, and the ammonia water dropping rate must be 10 cc / min (2% ammonia water conversion) or less.

This coprecipitate was washed with pure water by filtration to obtain Cu-A.
1 gel was obtained. This is autoclaved at 150 ℃
Was hydrothermally treated at the temperature of. The hydrothermally treated product was air-dried, then dried at 110 ° C. overnight and crushed in a mortar. This powder was calcined at 700 ° C. for 1 hour to synthesize a Cu-alumina hydrothermal treatment composite oxide catalyst (HTS-CuAlO).

The Cu-alumina hydrothermal treatment composite oxide catalyst and Na-type ZSM5 (NaZSM5) were used in a weight ratio of 50:
A physical mixture of 50 in a mortar was used as a mixed catalyst (HTS-CuAlO / NaZSM5).

(2) Performance test of mixed catalyst The NO _X purification activity was measured by a fixed bed atmospheric pressure flow reactor. The composition of the reaction gas is NO: 1000 ppm, C
₃ H ₆ : 1000 ppm, CO: 1200 ppm, H
₂ : 400 ppm, O ₂ : 6%, CO ₂ : 10%, H _{2
O: 10%, N 2:} Bal. And GHSV (space velocity)
Was performed at 200,000 h ^-1 . At this time, N ₂
No O formation was observed.

Table 5 and FIG. 5 show the test results. Note that FIG. 5 is a graph of the data in Table 5.

[0041]

[Table 5]

(3) Performance evaluation of mixed catalyst Cu alumina hydrothermal treatment complex oxide catalyst (HTS-CuA
It is found that the NO _x purification capacity of 10) decreases as the Cu content increases, but when mixed with zeolite, the NO _x purification capacity does not decrease up to 26%. This is because the hydrocarbon activated by the zeolite is NO _x.
It seems that the selective reduction reaction of is promoted.

(Embodiment 4) (1) Synthesis of mixed catalyst obtained by mixing zeolite and Co-alumina composite catalyst Co- was prepared in the same manner as in Embodiment 1 except that cobalt nitrate was used instead of aluminum nitrate. Alumina composite catalyst (CoAlO) was synthesized, and this was mixed with zeolite in a weight ratio of 50:50 to prepare a mixed catalyst (CoAlO).
O / NaZSM5) was obtained.

(2) Performance test of mixed catalyst The NO _X purification activity was measured by a fixed bed atmospheric pressure flow reactor. The composition of the reaction gas is NO: 1000 ppm, C
₃ H ₆ : 1000 ppm, CO: 1200 ppm, H
₂ : 400 ppm, O ₂ : 6%, CO ₂ : 10%, H _{2
O: 10%, N 2:} Bal. And GHSV (space velocity)
Was performed at 200,000 h ^-1 . At this time, N ₂
No O formation was observed.

Table 6 and FIG. 6 show the test results. Note that FIG. 6 is a graph showing the data in Table 6.

[0046]

[Table 6]

(3) Performance Evaluation of Mixed Catalyst As is apparent from the test results, it is understood that the NO _x purification ability is improved by mixing with the zeolite.

(Embodiment 5) Mixed catalyst (CuAlO /
The effect of the amount of zeolite mixed in NaZSM5) on the NO _x purification activity of the catalyst was tested.

The NO _X purification activity was measured by a fixed bed atmospheric pressure type reaction apparatus. The composition of the reaction gas is NO: 100
_{0ppm, C 3 H 6: 1000ppm} , CO: 1200
ppm, H ₂ : 400 ppm, O ₂ : 6%, CO ₂ : 1
_{0%, H 2 O: 10} %, N 2: Bal. And GHSV
The (space velocity) was 200,000 h ⁻¹ . At this time, generation of N ₂ O was not recognized.

Table 7 and FIG. 7 show the test results. Note that FIG. 7 is a graph of the data in Table 7.

[0051]

[Table 7]

From the test results, the mixed catalyst (CuAlO / N
It was found that the NO _x purification activity of aZSM5) was recognized in the range of 5 wt% or more and 95 wt% or less of the mixed amount of zeolite.

(Embodiment 6) Alumina composite catalyst (Cu
AlO) and NaZSM5 were separately pelletized and mixed into a suitable size, and the particle size dependence of the NO _x purification characteristics was measured. Table 8 and FIG. 8 show the results. Note that FIG. 8 is a graph of the data in Table 8. As a result, it was found that the particle size needs to be 1 mm or less.

[0054]

[Table 8]

(Embodiment 7) Mixed catalyst (CuAlO /
NaZSM5) and Cu ion exchange ZSM5 (exchange rate 10
0%) in the reaction gas over 80 hours over 80 hours
A 0 ° C heat durability test was performed. The composition of the reaction gas is NO: 1
_{000ppm, C 3 H 6: 1000ppm} , CO: 12
_{00ppm, H 2: 400ppm, O} 2: 6%, CO
₂ : 10%, H ₂ O: 10%, N ₂ : Bal. And GH
SV (space velocity) was performed at 200,000 h ^-1 .

Table 9 and FIG. 9 show the test results. Note that FIG. 9 is a graph of the data in Table 9.

[0057]

[Table 9]

From the test results, the mixed catalyst (CuAlO / N
It was found that no deterioration was observed in the thermal durability of aZSM5).

[0059]

As described above, according to the present invention, since the above-described configuration is adopted, the following effects are obtained.

(1) It is possible to obtain a mixed catalyst having an excellent NO _x purification ability especially in a steam atmosphere.

(2) It is possible to obtain a mixed catalyst having high heat resistance without irreversible deterioration of catalytic activity in a steam atmosphere.

[Brief description of the drawings]

FIG. 1 shows a mixed catalyst according to Embodiment 1 (CuAlO /
Graph showing the NO _x purification rate of NaZSM5)

FIG. 2 is a mixed catalyst (CuAlO / CuAlO) according to Embodiment 1.
Graph showing the NO _x purification rate of NaZSM5)

FIG. 3 is a mixed catalyst (CuO-γA) according to the second embodiment.
Graph showing the NO _x purification rate of P / NaZSM5)

FIG. 4 is a mixed catalyst (CuO-γA) according to the second embodiment.
Graph showing the NO _x purification rate of P / NaZSM5)

FIG. 5 is a mixed catalyst (HTS-Cu) according to the third embodiment.
Graph showing the NO _x purification rate of AlO / NaZSM5)

FIG. 6 is a mixed catalyst according to the fourth embodiment (CoAlO /
Graph showing the NO _x purification rate of NaZSM5)

FIG. 7 is a graph showing the NO _x purification rate depending on the mixed amount of zeolite in the mixed catalyst (CuAlO / NaZSM5).

FIG. 8 is a graph showing the NO _x purification rate according to the difference in particle size of the mixed catalyst.

FIG. 9 is a graph showing the thermal durability performance of a mixed catalyst (CuAlO / NaZSM5).

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location B01J 23/12 B01J 23/38 A 23/16 23/70 A 23/38 B01D 53/36 ZAB 23/70 102C

Claims (7)

[Claims] 1. An exhaust gas purifying catalyst comprising a mixture of zeolite and an alumina catalyst, a silica catalyst, or an alumina composite catalyst. 2. The exhaust gas purifying catalyst according to claim 1, wherein at least one of the mixed catalysts has a particle size of 1 mm or less. 3. The exhaust gas purifying catalyst according to claim 1, wherein an alumina carrying a transition metal is used as the alumina catalyst. 4. The exhaust gas purifying catalyst according to claim 1, wherein a silica carrying a transition metal is used as the silica catalyst. 5. The exhaust gas purifying catalyst according to claim 1, wherein an alumina composite oxide containing at least one transition metal and Al is used as the alumina composite catalyst. 6. The exhaust gas purifying catalyst according to claim 1, wherein the content of the transition metal in the alumina catalyst or the alumina composite catalyst is 15% or more and 45% or less. 7. The mixed amount of zeolite is 5 wt% or more, 9
The exhaust gas purifying catalyst according to claim 1, which is 5 wt% or less.