JPH1176829A - Manufacture of methane oxidation catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an ion exchange rate of a catalytic metal while a crystal structure of silicoaluminophosphate is prevented from being broken during exchange of the ion in the case where a silicoaluminophosphate material is a siliver catalyst, and a catalyst metal is supported by an ion exchange method inside an acid cite or a pore structure. SOLUTION: As a start substance for ion exchange, a salt of a catalytic metal of which an aqueous solution is likely to show weak acidity to basicity (for example, tetraminepalladium, etc.), or two or more kinds of salts of which the mixed solution is likely to indicate weak acidity to basicity are used, and the aqueous solution in which the salt is dissolved and silicoaluminophosphate material are mixed, heated, and stirred. Then, proton (H+) on the silicoaluminophosphate is exchanged in ion with a catalyst metal ion. Thereby, a precursor of an ion exchanged silicoaluminophosphate catalyst can be obtained, which is burnt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a methane oxidation catalyst for oxidizing unburned methane contained in exhaust gas of a lean burn gas engine.
The present invention relates to a method for producing a methane oxidation catalyst capable of efficiently oxidizing unburned methane discharged from a lean-burn gas engine even under exhaust gas conditions in which steam coexists, and maintaining high durability. .

[0002]

2. Description of the Related Art A gas engine is one of engines used for cogeneration in which heat is generated by utilizing gas combustion and its exhaust heat is used for heat demand such as cooling, heating and hot water supply. . Various types of gas engines have been developed, and if classified according to exhaust gas treatment technology, they can be divided into a three-way catalyst method and a lean combustion method.

[0003] The three-way catalyst method is a method in which three components of NOx, CO and HC are simultaneously treated with the same catalyst in a narrow range where the excess air ratio is close to one. On the other hand, the lean burn method burns gas in excess air, lowers the flame temperature, and suppresses the amount of NOx generated. Unlike the three-way catalyst method, the lean burn method does not require stopping the engine for catalyst replacement, has advantages such as high engine thermal efficiency and low initial cost.

[0004] However, the lean burn method has a drawback that although it has low NOx, it has a large amount of unburned components such as methane (CH ₄ ) contained in exhaust gas. There are no restrictions on unburned components such as methane (CH ₄ ) in exhaust gas, but they have a greenhouse effect about 21 times that of carbon dioxide (CO ₂ ). It is desirable to suppress as much as possible from the viewpoint of the global environment. Furthermore, if unburned components such as methane contained in the exhaust gas can be oxidized, the waste heat recovery efficiency can be improved by increasing the temperature of the exhaust gas, and there is also an economic merit. Therefore, various methods for producing an oxidation catalyst for oxidizing such unburned methane have been developed.

[0005] Among them, using a silico aluminophosphates _{((Si x Al y P z} ) O 2, hereinafter referred to as "SAPO") on the catalyst carrier, a method of supporting the catalyst metal by the ion exchange method, by immersion method alumina surface It is known that, compared to a conventional catalyst production method for supporting palladium and / or platinum, methane oxidation activity at low temperatures is excellent, and a high methane oxidation rate can be obtained with a smaller amount of noble metal carried.

For example, “76th CATSJ Mee
ting Abstracts, No. 1B08, p4
78 ”, SAPO is replaced with ammonium nitrate (NH ₄ N
O ₃ ) and ion exchange with ammonium ions (NH ₄ ⁺ ), followed by air calcination at 450 ° C. to form H-type (hereinafter referred to as “H
-SAPO ”), and then ion-exchanged (heated and stirred) using tetraamminedichloropalladium (Pd (NH ₃ ) ₄ Cl ₂ ) to obtain a precursor of a Pd ion-exchanged SAPO catalyst, which was then calcined. A method for doing so is disclosed.

[0007]

However, an aqueous solution of tetraamminedichloropalladium (Pd (NH ₃ ) ₄ Cl ₂ ) shows an acidity of about pH 4, and H-SAPO itself shows an acidity of about pH 4 in the aqueous solution. Therefore, the aqueous solution here has a pH of about 3. On the other hand, in the case of SAPO, under acidic conditions of about pH 3, the Si component is dissolved and the crystal structure of SAPO is destroyed. Therefore, it is necessary to adjust the catalyst while dropping aqueous ammonia to keep the pH of the aqueous solution at about 7. there were.

However, in the ion exchange, it is necessary to heat and agitate, but at that time, it is difficult to maintain the pH at about 7 because ammonia evaporates. ,
The catalyst performance will be reduced.

Also, under such acidic conditions, SAP
Palladium ion (P
Since d ²⁺ ) is exchanged again for protons (H ⁺ ), the palladium ion exchange rate decreases, and as a result, the oxidation activity of the methane oxidation catalyst decreases.

The present invention has been made in order to eliminate the above-mentioned disadvantages of the prior art, and an object of the present invention is to provide a method for supporting a noble metal catalyst on SAPO by an ion exchange method during ion exchange. An object of the present invention is to provide a method for producing a methane oxidation catalyst which prevents the crystal structure of SAPO from being destroyed and makes it possible to obtain an ion-exchange SAPO catalyst having excellent methane oxidation activity.

Another object of the present invention is to eliminate the step of dropping ammonia water during ion exchange, and to simplify the process for producing an ion-exchange SAPO catalyst.

Still another object is to prevent the catalytic noble metal ions from being exchanged with protons again during ion exchange,
It is to improve the ion exchange rate of a catalytic noble metal.

Another object is to use an ion exchange method for SA.
By supporting various noble metal catalysts and cocatalysts on PO in combination, it is possible to prevent the crystal structure of SAPO from being destroyed during ion exchange and to produce a methane oxidation catalyst having excellent oxidation activity and durability. It is an object of the present invention to provide a method for producing a methane oxidation catalyst.

[0014]

In order to achieve this object, the invention according to claim 1 uses a silicoaluminophosphate-based material as a catalyst carrier, and comprises an acid site or pore structure in the catalyst carrier of the silicoaluminophosphate-based material. Within
In a method for producing a methane oxidation catalyst supporting a catalytic metal by an ion exchange method, a salt of a catalytic metal exhibiting weak acidity to basicity in an aqueous solution is used as a starting material, and an aqueous solution in which the salt is dissolved and a silicoaluminophosphate-based material are used. Are mixed and heated and stirred, and a proton (H ⁺ ) on the silicoaluminophosphate is ion-exchanged with a catalytic metal ion to obtain a precursor of an ion-exchange silicoaluminophosphate-based catalyst, which is calcined. It is the gist. This makes it possible to prevent the crystal structure of SAPO from being destroyed and to improve the ion exchange rate without taking measures such as dropping ammonia water during ion exchange.

The SAPO used in the present invention is obtained by substituting Al and P of aluminophosphate (AlPO ₄ ) with Si, and thus has an acid point in the framework of the aluminophosphate. It is a kind of molecular sieve that shows ion exchange phenomenon. The present invention utilizes the ion exchange phenomenon to highly support a noble metal catalyst in the acid sites or pore structure of SAPO.

SAPO is synthesized by preparing an aqueous mixture containing a phosphorus source, an aluminum source, a silicon source and an organic template, and performing a hydrothermal reaction at a temperature of 100 to 250 ° C. in a closed pressure vessel. Usually, orthophosphoric acid is used as the phosphorus source, pseudoboehmite, aluminum alkoxide, etc., as the aluminum source, silica sol, fused silica, amorphous precipitated silica, silica gel, silicon alkoxide, etc., as the silicon source, and as the organic template, , Amines, and quaternary ammonium compounds.

The organic template is a type that forms pores during crystal growth, and SAPO having various crystal structures can be synthesized depending on the organic template used. For example, when tetrapropylammonium is used as an organic template, 0.7 to 0.8 nm
AFI type “SAPO-5” having a pore diameter of
When n-propylamine is used, an AEL-type “SAPO-11” having a pore diameter of 0.6 nm is used. When tetraethylammonium is used, a chabazite-type “SAPO-34” having a pore diameter of 0.4 nm is used. Is obtained. What kind of crystal structure SAPO is used as a catalyst carrier needs to appropriately select an optimum one depending on the type of catalyst.

The starting material used for carrying out the ion exchange must have an aqueous solution which exhibits a weak acidity to a basicity, preferably a pH of 7 or more. That is, H-SAPO from which the organic template has been removed by baking exhibits acidity of about pH 4 in an aqueous solution itself. Meanwhile, SAP
O has a property that the Si component is dissolved under acidic conditions of about pH 3 and the crystal structure is destroyed. Therefore, when the aqueous solution is ion-exchanged using a salt having a pH of less than 4, mixing the aqueous solution in which the salt is dissolved with H-SAPO results in a pH of the aqueous solution of about 3, which adversely affects SAPO. Because it becomes.

The starting material for supporting the noble metal catalyst on the SAPO by the method of the present invention is tetraammine palladium hydroxide (Pd (NH ₃ ) ₄ (OH)
₂ ) and tetraammine platinum hydroxide (Pt (NH ₃ )
It is particularly desirable to use one or both substances selected from the group consisting of ₄ (OH) ₂ ) (claim 2).

Palladium (Pd) and platinum (Pd) are used as catalyst metals for efficiently oxidizing methane having a high ignition point.
t) is effective. Particularly, it is known that when palladium and platinum are combined and supported, methane oxidation activity and durability in the coexistence of steam are remarkably improved. , The pH becomes about 7 even when the aqueous solution is mixed with SAPO.
Is not adversely affected. Also, the pH of the aqueous solution
Is about 7, and since there is almost no proton in the system, the cation is only palladium ion, and the ion exchange rate is improved.

The invention according to claim 3 uses both a salt of a catalytic metal exhibiting basicity and a salt of a catalytic metal exhibiting acidity in an aqueous solution as a starting material, and the aqueous solution has a weak acidity.
The gist is that the starting material is dissolved so as to be basic, and ion exchange is performed using the aqueous solution.

The third aspect of the invention is also based on the same concept as the first aspect of the invention. In short, the purpose of the invention is to improve the initial activity and durability of the methane oxidation catalyst by using SAPO. When two or more catalyst metals are supported by an ion exchange method, the aqueous solution is used in combination with a salt exhibiting basicity and a salt exhibiting acidity, so that the aqueous solution used for ion exchange is kept weakly acidic to basic. This prevents the pH of the aqueous solution when H-SAPO is added from becoming 3 or less, thereby preventing the crystal structure of SAPO from being destroyed during ion exchange and improving the ion exchange rate. is there.

Here, as a starting material showing basicity in the aqueous solution, tetraammine palladium hydroxide (Pd
One or both substances selected from the group consisting of (NH ₃ ) ₄ (OH) ₂ ) and tetraammine platinum hydroxide (Pt (NH ₃ ) ₄ (OH) ₂ ) Starting materials shown include palladium nitrate (Pd (NO ₃ ) ₂ ),
Tetraamminedichloropalladium (Pd (NH ₃ ) ₄ C
l ₂ ), tetraamminepalladium nitrate (Pd (NH
₃ ) ₄ (NO ₃ ) ₂ ), tetraamminedichloroplatinum (Pt
(NH ₃ ) ₄ Cl ₂ ), tetraammineplatinum nitrate (Pt
(NH ₃ ) ₄ (NO ₃ ) ₂ ), lanthanum acetate (La (OCO
CH ₃ ) ₃ ), lanthanum nitrate (La (NO ₃ ) ₃ ), lanthanum oxalate (La ₂ (C ₂ O ₄ ) ₃ ), cerium acetate (C
e (OCOCH ₃ ) ₃ ), cerium nitrate (Ce (N
O ₃ ) ₃ ) and cerium oxalate (Ce ₂ (C ₂ O ₄ ) ₃ )
One or more substances selected from the group consisting of the above are particularly desirable (claim 4).

For example, when palladium and platinum are combined and supported on SAPO, both may be ion-exchanged using a salt exhibiting basicity (claim 2). For platinum, salts exhibiting acidity such as platinum nitrate, tetraamminedichloroplatinum, and tetraammineplatinum nitrate can be used. Conversely, when a salt showing acidity for palladium is used, a salt showing basicity for platinum may be used.

Although lanthanum and cerium alone have almost no action as a methane oxidation catalyst,
By supporting it on SAPO at the same time as palladium and platinum, it has a function as a co-catalyst that further enhances the initial activity and durability of palladium and platinum. In particular, it has the effect of significantly improving the methane oxidation activity and durability in the presence of steam.

The lanthanum and cerium salts used for ion exchange are desirably those which show basicity in an aqueous solution, like palladium and the like. However, tetraammine palladium hydroxide (Pd (NH ₃ ) ₄ (OH) ₂ ) and / or tetraammineplatinum water salt _{(Pt (NH 3) 4 (} OH) 2) when added to the aqueous solution at the same time, it is possible to use lanthanum and acetates of cerium, nitrate or oxalate. Although they exhibit acidity in an aqueous solution, they have a pH of about 6 to 7 as a whole when used in combination with tetraammine palladium hydroxide, etc., so that they do not significantly affect SAPO during ion exchange. It is.

Next, an example of a method for producing a methane oxidation catalyst according to the present invention will be described. First, the shape of the catalyst carrier may be a honeycomb-shaped catalyst carrier using commercially available SAPO itself as a raw material, or a granular carrier sized to about 16 to 60 mesh. Alternatively, a honeycomb-shaped substrate may be prepared using cordierite or the like as a raw material, and a fine powder of SAPO may be wash-coated thereon.

Next, such a carrier is converted to a palladium salt,
It is immersed in an aqueous solution containing a platinum salt or the like to perform ion exchange under a predetermined condition. At that time, according to the method of the present invention, since the aqueous solution is kept weakly acidic to basic, it is not necessary to drop ammonia water, and the process can be simplified. After completion of ion exchange, the mixture was filtered, washed with pure water, dried,
After reduction, calcination is further performed in an oxygen stream to obtain a methane oxidation catalyst.

When lanthanum or cerium is supported on SAPO, it is necessary to first perform ion exchange using an aqueous solution containing a palladium salt or the like, and then add an aqueous solution of a lanthanum salt or cerium salt. This is because when a lanthanum salt or the like is added simultaneously with a palladium salt or the like, lanthanum or cerium is selectively ion-exchanged, and the amount of palladium and platinum carried decreases.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. (Example 1) As a catalyst carrier, SAPO-11 (UOP
Baked at 600 ° C. for 6 hours in an oxygen stream to remove impurities such as an organic template, and then tetraammine palladium hydroxide (Pd (N
_{H 3) 4 (OH) 2} ) were mixed with an aqueous solution, 6-12 at 80 ° C.
Ion exchange was performed for hours. Next, the mixture was filtered, washed with pure water, dried at 120 ° C. for 12 hours, further reduced at 300 ° C. for 3 hours in a stream of hydrogen, and then dried in a stream of oxygen at 600 ° C. for 3 hours.
Baking at 6 ° C. for 6 hours, Pd ion exchange SAP
O (hereinafter, referred to as “Pd-SAPO-11 (O)”) was prepared.

Comparative Example 1 As a palladium source, tetraammine palladium nitrate (Pd (NH ₃ ) ₄ (N
O ₃ ) ₂ ) or tetraamminedichloropalladium (Pd
Except for using (NH ₃ ) ₄ Cl ₂ ), a Pd ion-exchanged SAPO (hereinafter referred to as “Pd-SAPO-11 (N)” and “Pd-SAPO,” respectively) was used in the same procedure as in Example 1.
-11 (C) ").

The amount of palladium carried on each of the obtained catalysts was measured. Table 1 shows the results.

[0033]

[Table 1]

In each catalyst, the amount of palladium ion charged was 1.20% by weight, whereas the actual amount of ion exchange was 1.22% by weight for Pd-SAPO-11 (O) according to the method of the present invention. there were. On the other hand, Pd-SAPO-1
1 (N) and Pd-SAPO-11 (C) were 0.80% by weight and 0.38% by weight, respectively.

Next, these Pd ion-exchanged SAPOs are molded, crushed and sized to 16 to 60 mesh, and
g was packed in a reaction tube and fired in air at 600 ° C. for 2 hours. Further, after the temperature was lowered to a predetermined temperature, a reaction test was performed to examine the initial activity of the Pd ion exchanged SAPO catalyst.

The reaction test was carried out using an atmospheric pressure fixed bed flow type reaction test apparatus at a test temperature of 250 to 600 ° C. and a reaction gas containing no steam (methane (CH ₄ ) = 4000 pp).
m, carbon monoxide (CO) = 500 ppm, carbon dioxide (CO ₂ ) = 5%, steam (H ₂ O) = 0%, and the balance nitrogen (N ₂ )) at a flow rate of 5000 ml / hr. The results are shown in FIG.

Over the entire temperature range, the methane oxidation rate of Pd-SAPO-11 (O) by the method of the present invention was the highest, followed by Pd-SAPO-11 (N) and Pd-SAP.
The order was O-11 (C).

From the above results, when tetraammine palladium hydroxide (Pd (NH ₃ ) ₄ (OH) ₂ ) which exhibits basicity in an aqueous solution is used as a palladium source, the case where a salt which exhibits acidity in an aqueous solution is used It was found that the ion exchange amount and the methane oxidation rate were superior to those of the above.

(Example 2) First, as a preliminary experiment, a test for specifying the most suitable SAPO as a catalyst carrier was performed.

As the catalyst carrier, three types of SAPO having different crystal structures (SAPO-5 (manufactured by Mizusawa Chemical Industries, the same applies hereinafter), SAPO-11, and SAPO-34 (UOP
)), Except that) was used.
Various Pd ion-exchanged SAPOs carrying 1% by weight of palladium were prepared, and subjected to a reaction test in the same procedure as in Example 1. The reaction test conditions were the same as those in Example 1, and a reaction gas containing water vapor (methane (CH ₄ ) = 400)
0 ppm, carbon monoxide (CO) = 500 ppm, carbon dioxide (CO ₂ ) = 5%, water vapor (H ₂ O) = 10%, and the remaining nitrogen (N ₂ ). The results are shown in FIG.

In the absence of steam, SAPO-11 = SA
PO-5> SAPO-34 shows higher activity in the order of
At a low temperature of 0 ° C., SAPO-11 and SAPO-5
Methane oxidation rate exceeded 95%. However, in the presence of 10% steam, the activity was significantly reduced, and the reaction temperature was 400 ° C.
Methane oxidation rate in SAPO-5 (65.1%)
> SAPO-11 (28.4%)> SAPO-34 (2
4.3%). From these results, it was found that SAPO-5 was the most excellent catalyst carrier for supporting palladium.

Next, the procedure of Example 1 was repeated, except that SAPO-5 was selected as the catalyst carrier and tetraamminepalladium hydroxide and / or tetraammineplatinum hydroxide was used as the catalyst noble metal source. weight%
And Pd-Pt ion exchange S carrying 1% by weight of platinum
APO (1% Pd-1% Pt-SAPO-5), Pd ion-exchanged SAPO supporting 1% by weight of palladium (1
% Pd-SAPO-5) and Pt ion-exchanged SAPO carrying 1% by weight of platinum (1% Pt-SAPO-5)
Was prepared respectively.

After molding these ion-exchange SAPOs obtained, they were pulverized and sized to 16 to 60 mesh.
Was packed in a reaction tube and calcined at 600 ° C. for 2 hours in the air.
Further, after the temperature was lowered to a predetermined temperature, a durability test was performed.

The endurance test was carried out using an atmospheric pressure fixed bed flow type reaction test apparatus at a test temperature of 400 ° C., a test time of 40 hours, and a reaction gas containing water vapor (methane (CH ₄ ) = 400).
0 ppm, carbon monoxide (CO) = 500 ppm, carbon dioxide (CO ₂ ) = 5%, water vapor (H ₂ O) = 10%, and the balance nitrogen (N ₂ )) at a flow rate of 5000 ml / hr. . For comparison, a durability test was similarly performed on a reaction gas containing no water vapor at all.
The results are shown in FIG.

The 1% Pd-SAPO-5 catalyst showed a high methane oxidation rate of 95% or more even after 40 hours when the reaction gas containing no water vapor was used. However, in the case of the reaction gas containing water vapor, the methane oxidation rate rapidly decreased to 40 to 50% at the beginning of the test time, and further decreased to about 20% after 40 hours of durability. In addition, 1% Pt-SAPO
The -5 catalyst showed almost no methane oxidation activity from the beginning, and the methane oxidation rate was 5% or less. On the other hand, 1% Pd
In the -1% Pt-SAPO-5 catalyst, the methane oxidation rate decreased from 68% to about 50% at the beginning of the test time, but thereafter the methane oxidation rate was stabilized, and the high methane oxidation rate of 40% or more was maintained after 40 hours of durability. Rate.

From the above results, when palladium and platinum are compositely supported on SAPO according to the method of the present invention, compared with the case where palladium is supported alone, a low temperature region corresponding to the actual exhaust gas temperature (around 400 ° C.) ), And showed high durability even under exhaust gas conditions in which water vapor coexists.

Further, in the catalyst in which only platinum was supported at 1% by weight, almost no methane oxidation activity was exhibited under the condition that water vapor coexists and the exhaust gas temperature was low. By carrying it,
It has been found that even if the amount of supported platinum is small, the initial activity and durability are remarkably improved.

Example 3 As a catalyst carrier, SAPO-
5 and calcination in an oxygen stream at 600 ° C. for 6 hours to remove impurities such as an organic template, and then mixing them with an aqueous solution containing tetraammine palladium hydroxide and tetraammine platinum hydroxide, respectively. Ion exchange was performed at 80 ° C. for 6 hours. Then, lanthanum acetate (La (OCOCH ₃ )) or cerium acetate (Ce (O
An aqueous solution of COCH ₃ )) was added, and ion exchange was further performed at 80 ° C. for 6 hours.

Next, the mixture was filtered and washed with pure water.
Dry at 20 ° C for 12 hours, and further in a hydrogen stream at 300 ° C.
And then calcined at 600 ° C. for 6 hours in an oxygen stream to obtain 1% by weight of palladium and 1% by weight of platinum.
And Pd-Pt-La ion-exchange SAPO catalyst supporting 1% by weight of lanthanum (1% Pd-1% Pt-1% La
-SAPO-5) and Pd-Pt-C supporting 1% by weight of palladium, 1% by weight of platinum and 1% by weight of cerium
e-ion exchange SAPO catalyst (1% Pd-1% Pt-1%
Ce-SAPO-5) was prepared respectively.

For comparison, a Ce ion-exchanged SAPO catalyst (1% Ce-SAPO-5) supporting only 1% by weight of cerium was prepared according to the same procedure as described above.

The resulting ion-exchanged SAPO was molded, pulverized and sized to 16 to 60 mesh.
Was packed in a reaction tube and calcined at 600 ° C. for 2 hours in the air.
After the temperature is lowered to a predetermined temperature, water vapor is
%, A durability test was performed in the same procedure as in Example 2. FIG. 4 shows the results.

1% Ce-SAPO-5 showed almost no methane oxidation activity, but 1% Pd-1% Pt-S
1% by weight of cerium was further supported on APO-5.
In the case of% Pd-1% Pt-1% Ce-SAPO-5, the methane oxidation rate exceeded 80% at the beginning of the test time, and showed a high methane oxidation rate of about 60% even after 40 hours of durability.

Further, 1% Pd-1% Pt-1% La-S
APO-5 also has a methane oxidation rate of 80% or more at the beginning of the test time and a methane oxidation rate of about 5 even after 40 hours of durability.
0%, and 1% P produced in Example 2
d-1% showed higher initial activity and durability than Pt-SAPO-5.

From the above results, when the palladium and platinum are supported on SAPO in a composite manner by the method of the present invention and lanthanum or cerium is further supported, the 1% Pd-1% Pt-SAPO-5 catalyst in Example 2 is obtained. than,
Furthermore, the initial activity in a low temperature region (around 400 ° C.) is high,
Also, it was found that high durability was exhibited even under exhaust gas conditions in which steam coexisted.

Further, the catalyst loaded with only 1% by weight of cerium showed almost no methane oxidation activity under the condition that water vapor coexists and the temperature of the exhaust gas was low. In addition, when lanthanum or cerium is compositely supported, even if the amount of lanthanum or cerium supported is small, the initial activity and durability are remarkably improved. I understand.

(Comparative Example 2) A 1% Pd / alumina catalyst having 16% to 60 mesh of alumina as a catalyst carrier and supporting 1% by weight of palladium by an immersion method, and 1%
1 loaded with weight% palladium and 1 weight% platinum
% Pd-1% Pt / alumina catalyst was prepared, respectively.
With respect to each of the obtained catalysts, a reaction test was performed on a reaction gas containing 10% water vapor by the same procedure as the preliminary experiment in Example 2. FIG. 5 shows the results.

The conventional 1% Pd / alumina catalyst can be obtained by using the 1% Pd-SAPO according to the present invention over the entire temperature range.
The methane oxidation rate is lower than that of the -5 catalyst, and at 400 ° C. corresponding to the exhaust gas temperature of the gas engine, the latter 65.
The former was only 10.8% compared to 1%. In addition, for the 1% Pd / alumina catalyst, in which 1% platinum is further supported on the 1% Pd-1% Pt / alumina catalyst, the increase in the methane oxidation rate is slight, and the methane oxidation rate at 400 ° C. It was 14.3%.

The above results indicate that in the conventional method for producing a catalyst by the immersion method using alumina as a catalyst carrier, in order to obtain a low catalytic activity at low temperatures and a high methane oxidation rate,
This indicates that it is necessary to increase the amount of supported catalyst. In addition, in the conventional method for producing a catalyst, since the catalyst noble metal cannot be supported in a highly dispersed state, the loading amounts of palladium and platinum are each 1%.
It shows that the compounding effect is hardly recognized when the loading amount is low.

On the other hand, the above results indicate that SA
Ion exchange using PO under conditions where the aqueous solution becomes weakly acidic to basic is extremely important for significantly reducing the consumption of catalytic noble metal. Further, from FIG. 3 and FIG. As is evident, when platinum, cerium and the like are compositely supported in addition to palladium, a remarkable composite effect is exhibited even when the amount of supported catalyst is small, and high methane which cannot be obtained by the conventional catalyst production method is obtained. This shows that a methane oxidation catalyst having oxidation activity and durability can be obtained.

The present invention is not at all limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, even if the SAPO itself is made into a honeycomb shape, or a honeycomb-shaped base material is made of cordierite or the like, the SAPO is wash-coated thereon, and then palladium or the like is supported by an ion exchange method. Similar effects can be obtained.

In the above embodiment, the amount of the noble metal carried is set to 1% by weight. However, the present invention is not limited to this, and the initial activity and durability can be further improved by increasing the amount of the noble metal carried. Therefore, the optimal amount of the catalyst may be appropriately selected from the viewpoint of cost effectiveness.

[0062]

According to the present invention, SAPO is produced by ion exchange.
In the case of supporting a noble metal catalyst on the top, since a method in which the aqueous solution is subjected to ion exchange using a starting material exhibiting weak acidity to basicity is employed, the crystal structure of SAPO is prevented from being destroyed during ion exchange, There is an effect that an ion exchange SAPO catalyst having excellent methane oxidation activity can be obtained.

Further, the step of dropping ammonia water during ion exchange is not required, and the effect of simplifying the production process of the ion exchange SAPO catalyst is obtained.

Furthermore, since the catalytic noble metal ions are prevented from being exchanged with protons again during the ion exchange, the ion exchange rate of the catalytic noble metal is improved, thereby reducing the cost of the methane oxidation catalyst. effective.

Further, a substance whose aqueous solution is basic and a substance whose acidity is acidic are used, and their mixture is weakly acidic to
Since various noble metal catalysts, cocatalysts, and the like are compositely supported on the SAPO by the ion exchange method under the condition of being basic, the crystal structure of the SAPO is prevented from being destroyed during the ion exchange. In addition, there is an effect that a methane oxidation catalyst having high oxidation activity and durability, which cannot be obtained by the conventional production method, can be produced.

[Brief description of the drawings]

FIG. 1. Pd-SAPO-1 prepared with various Pd raw materials
It is a figure which shows the methane oxidation activity of one catalyst.

FIG. 2 shows the initial activity of various Pd-SAPO catalysts for methane oxidation.

FIG. 3 is a graph showing a change over time in catalytic activity of a Pd-Pt-SAPO catalyst according to the present invention.

FIG. 4 is a diagram showing the change over time in the catalytic activity of a Pd-Pt-Ce-SAPO catalyst and a Pd-Pt-La-SAPO catalyst according to the present invention.

FIG. 5 is a diagram showing the initial activity of a conventional catalyst for methane oxidation.

Claims (4)

[Claims] 1. A method for producing a methane oxidation catalyst comprising: using a silicoaluminophosphate-based material as a catalyst carrier; and supporting a catalyst metal by an ion exchange method in an acid site or a pore structure in the catalyst carrier of the silicoaluminophosphate-based material. Using a salt of a catalyst metal exhibiting weak acidity to basicity in an aqueous solution as a starting material, mixing an aqueous solution in which the salt is dissolved and a silicoaluminophosphate-based material, stirring with heating,
An ion-exchange silicoaluminophosphate-based catalyst precursor is obtained by ion-exchanging protons (H ⁺ ) on silicoaluminophosphate with catalytic metal ions, and the precursor is calcined. Production method. 2. The starting material is selected from the group consisting of tetraammine palladium hydroxide (Pd (NH ₃ ) ₄ (OH) ₂ ) and tetraammine platinum hydroxide (Pt (NH ₃ ) ₄ (OH) ₂ ). The method for producing a methane oxidation catalyst according to claim 1, wherein the one or both substances are selected. 3. A catalyst metal salt showing basicity and an acidic catalyst metal salt in an aqueous solution are used as a starting material, and the starting material is dissolved so that the aqueous solution becomes weakly acidic to basic. 2. The method for producing a methane oxidation catalyst according to claim 1, wherein the aqueous solution is subjected to ion exchange. 4. A starting material showing basicity in said aqueous solution is tetraammine palladium hydroxide (Pd (NH ₃ ) ₄
(OH) ₂ ) and tetraammine platinum hydroxide (Pt (N
One or both substances selected from the group consisting of H ₃ ) ₄ (OH) ₂ ) and the acidic starting substance in the aqueous solution is palladium nitrate (Pd (NO ₃ ) ₂ ), tetraamminedichloropalladium (Pd (NH ₃ ) ₄ Cl ₂ ), tetraammine palladium nitrate (Pd (NH ₃ ) ₄ (N
O ₃ ) ₂ ), tetraamminedichloroplatinum (Pt (N
H _{3) 4} Cl _2), tetraammine platinum nitrate (Pt (N
H ₃ ) ₄ (NO ₃ ) ₂ ), lanthanum acetate (La (OCOCH)
₃ ) ₃ ), lanthanum nitrate (La (NO ₃ ) ₃ ), lanthanum oxalate (La ₂ (C ₂ O ₄ ) ₃ ), cerium acetate (Ce (O
COCH ₃ ) ₃ ), one or more substances selected from the group consisting of cerium nitrate (Ce (NO ₃ ) ₃ ) and cerium oxalate (Ce ₂ (C ₂ O ₄ ) ₃ ) The method for producing a methane oxidation catalyst according to claim 3, wherein