JP3244935B2 - Combustible gas combustion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of burning a combustible gas, for example, a gas such as carbon monoxide, hydrogen, or a hydrocarbon, using a catalyst. The present invention relates to a catalytic combustion method capable of stably burning at room temperature.

[0002]

2. Description of the Related Art Conventionally, a catalytic combustion method for obtaining a high-temperature gas by using a lower hydrocarbon gas such as methane as a fuel and performing a combustion reaction in a diluted state generally not within the combustion condition range has been conventionally used. More known. As a combustion catalyst in the conventional method, a ceramic such as honeycomb cordierite or mullite is used as a base material, and alumina, silica, titania, zirconia alone or at least two or more of these oxides are used as a base material. There has been proposed a catalyst which is coated with a support containing a composite oxide consisting of and supports a noble metal oxide such as palladium oxide as an active ingredient. More recently, noble metal oxides such as palladium oxide have been supported as active ingredients on a carrier containing alumina, silica, titania, zirconia alone or a composite oxide of at least two of these oxides. The catalyst obtained by coating the heat-resistant substrate with the powder thus obtained is disposed at the front stage of the combustible gas flow path, and at the subsequent stage, alumina, silica, titania, zirconia alone or at least two oxides of these oxides are used. There has been proposed a method of disposing a catalyst in which a noble metal oxide such as palladium oxide and magnesia are coated on a heat-resistant base material on a support containing a composite oxide composed of and a rare earth element oxide. (Japanese Patent Application No. 04-320452, 05
-12340, 05-122341)

[0003]

However, in the above-described combustible gas combustion method, a catalyst using a carrier not containing an oxide of a rare earth element, which is used in the preceding stage of the combustible gas flow path, Although it has excellent low-temperature ignitability, it has a problem that palladium oxide is apt to aggregate at 800 ° C. or higher, and the activity decreases with time. The present invention has been made in view of the above technical level, and provides a method capable of burning a combustible gas even at a low temperature and stably performing complete oxidation combustion even at a high temperature.

[0004]

According to the present invention, a composite oxide comprising at least two oxides of oxides of alumina, silica, titania and zirconia and a rare earth element are oxidized before a combustible gas flow path. A catalyst in which palladium oxide-supported powder is coated on a carrier containing a substance, and a heat-resistant substrate is coated with a catalyst, and at the subsequent stage of the catalyst, at least two oxides of oxides of alumina, silica, titania, and zirconia are used. A catalyst comprising a heat-resistant base material coated with a powder comprising magnesia, zirconia and at least one oxide of rare earth oxides and palladium oxide supported on a support containing a composite oxide comprising the oxides of rare earth elements and an oxide of a rare earth element. And combusting the combustible gas.

The catalyst referred to in the present invention refers to at least two oxides of alumina, silica, titania and zirconia.
Palladium oxide is added in an amount of 1% by weight to 7% to a support containing a composite oxide composed of at least one kind of oxide and an oxide of a rare earth element.
0% by weight (based on the total weight of the catalyst powder) of the supported catalyst powder or palladium oxide and 1 to 30% by weight of at least one oxide of oxides of magnesia, zirconia and rare earth elements (total of the catalyst powder) Weight basis)
It means that the supported catalyst powder is wash-coated on a honeycomb-type substrate made of a heat-resistant ceramic such as mullite, cordierite, aluminum titanate, zirconia, or zirconia spinel. When the catalyst powder is wash-coated on the honeycomb substrate, the coating amount is preferably in the range of 20 to 500 parts by weight of the catalyst powder per liter of the honeycomb substrate. In addition, the carrier referred to in the present invention is a composite oxide 100 comprising at least two oxides of oxides of alumina, silica, titania and zirconia.
It contains an oxide of a rare earth element in a range of 1 to 30 parts by weight per part by weight.

[0006]

In the catalytic combustion method for combustible gas of the present invention,
In the former stage (gas inlet side), palladium oxide as an active component was carried on a carrier containing a composite oxide comprising at least two oxides of oxides of alumina, silica, titania and zirconia and an oxide of a rare earth element. A catalyst coated with a powder on a heat-resistant base material, a catalyst coated on a heat-resistant base material with a powder supporting at least one oxide and palladium oxide of magnesia, zirconia and an oxide of a rare earth element on the carrier at a later stage. Because of the arrangement, palladium oxide can be stably burned even at a high temperature of 800 ° C. or higher where aggregation of palladium oxide is likely to occur. Taking the example of methane combustion, which is the least flammable, as an example, oxidization of methane is started at 400 ° C. or less by the former catalyst, and the temperature of the former catalyst layer wall surface is reduced to 11 ° C.
By controlling the temperature of the wall surface of the subsequent catalyst layer to be equal to or less than 1200C, it is possible to always maintain stable combustion. Hereinafter, the present invention will be described specifically with reference to examples.

[0007]

EXAMPLE 250 g of a titanium tetrachloride solution is dissolved in ion-exchanged water, and ion-exchanged water is added so that the pH becomes 3. Next, 315 g of γ-alumina was added, and after stirring for 3 hours,
Ammonia water is added dropwise until pH = 9. After stirring for 1 hour, the precipitate was filtered and washed with ion-exchanged water. Further, it is dried in a drier all day and night, baked in an electric furnace at 500 ° C. for 5 hours, and baked at 1000 ° C. for 24 hours to obtain a titania-alumina composite oxide (TiO ₂ : Al ₂ O ₃ = 25:
(75 weight ratio). This powder was immersed in an aqueous solution of neodymium nitrate, dried at 120 ° C., baked at 500 ° C. for 5 hours, and baked at 1000 ° C. for 24 hours to obtain neodymium oxide per 100 parts by weight of titania-alumina composite oxide.
Carrier 1 supporting 0 parts by weight was prepared. The support 1 was immersed in an aqueous solution of palladium nitrate, dried, calcined at 500 ° C. for 5 hours, and calcined at 1000 ° C. for 10 hours to prepare a catalyst powder 1 supporting 10% by weight of palladium oxide with respect to the catalyst powder.

[0008] Zirconium oxychloride 106g ion
Dissolve in exchanged water and ion-exchanged water until pH = 2
Add. Next, 365 g of γ-alumina was added and stirred for 3 hours.
After stirring, aqueous ammonia is added dropwise until pH = 9. 1
After stirring for a period of time, the precipitate was filtered and washed. further
Dry in a drier all day and night and fire in an electric furnace at 500 ° C for 5 hours
After that, it is baked at 1000 ° C. for 24 hours to make zirconia-aluminum.
Complex oxide (ZrO _Two: Al_TwoO_Three= 10: 90 weight
Powder) was obtained. This powder is immersed in an aqueous cerium nitrate solution.
After immersion, drying at 120 ° C and baking at 500 ° C for 5 hours, 1
Calcined at 000 ° C for 24 hours, 20 parts by weight of cerium oxide
A supported carrier 2 was prepared. Carrier 2 is palladium nitrate water
After immersing in a solution and drying, baking at 500 ° C. for 5 hours, 10
Firing at 00 ° C for 10 hours, oxidation based on the total weight of catalyst powder
A catalyst powder 2 carrying 30% by weight of palladium was prepared.
Was.

131 g of zirconium oxychloride is ionized
Dissolve in exchanged water and ion exchange to pH 2.5.
Add water replacement. Next, 150 g of silica powder is added, and 3 hours
After stirring, aqueous ammonia is added dropwise until pH = 9.
After stirring for 1 hour, the precipitate was filtered and washed. Further
Dried in a drier all day and night and baked in an electric furnace at 500 ° C for 5 hours.
After firing, sintering at 1000 ° C for 24 hours
Complex oxide (ZrO _Two: SiO_Two= 25: 75 weight
Powder) was obtained. This powder is immersed in an aqueous lanthanum nitrate solution.
Soak and dry at 120 ° C, bake at 500 ° C for 5 hours,
Calcined at 000 ° C for 24 hours to obtain 15 parts by weight of lanthanum oxide
A supported carrier 3 was prepared. Carrier 3 is palladium nitrate water
After immersing in a solution and drying, baking at 500 ° C. for 5 hours, 10
Firing at 00 ° C for 10 hours, oxidation based on the total weight of catalyst powder
Catalyst powder 3 carrying 20% by weight of palladium was obtained.

[0010] 52 g of zirconium oxychloride and 53 g of lanthanum nitrate are dissolved in ion-exchanged water, and ion-exchanged water is added so that pH = 3. Next, γ-alumina 16
After adding 0 g and stirring for 3 hours, aqueous ammonia is added dropwise until pH = 9. After stirring for 1 hour, the precipitate was filtered and washed. Further, it is dried in a drier all day and night, and calcined in an electric furnace at 500 ° C. for 5 hours, and calcined at 1000 ° C. for 24 hours to obtain carrier 4 (La ₂ O ₃ : ZrO ₂ : Al ₂ O ₃ = 10:
10:80 weight ratio). The carrier 4 is immersed in an aqueous solution of palladium nitrate, dried, and calcined at 500 ° C. for 5 hours.
Calcined at 1000 ° C. for 10 hours, based on the total weight of the catalyst powder,
Catalyst powder 4 carrying 50% by weight of palladium oxide was obtained.

The above-mentioned catalyst powders 1 to 4 are wash-coated on a cordierite honeycomb substrate having 200 openings per square inch (200 cells / inch ² ),
After calcination at 500 ° C. for 5 hours, calcination was performed at 1000 ° C. for 24 hours to obtain Catalysts 1 to 4. The coating amount of the catalyst powders 1 to 4 per liter of the honeycomb substrate was 200 parts by weight.

Next, the carriers 1 to 4 prepared by the above method
Each of them was mixed with an aqueous solution of palladium nitrate and
C, magnesium nitrate, zirconium nitrate, lanta nitrate
Cerium nitrate, neodymium nitrate aqueous solutions, or
Mixing a mixed aqueous solution of cerium nitrate and magnesium nitrate
Dipped in the solution, dried at 120 ° C.,
After baking for 1000 hours, bake at 1000 ° C for 10 hours.
Catalyst containing oxides of a, zirconia and rare earth elements
Powders 5 to 10 (compositions are shown in Table 1) were prepared. Catalyst powder
The last 5 to 8 are 200 cells / inch^TwoMade of cordierite
Wash coat on honeycomb substrate, 5 hours at 500 ℃
After calcination, calcined at 1000 ° C. for 24 hours to obtain catalysts 5 to 8.
Was. In addition, 1 liter of honeycomb substrate of catalyst powders 5 to 8 was used.
The amount of coating was 300 parts by weight. Also, catalyst powder
Ends 9 and 10 are 60 cells / inch ^TwoMade of cordierite
Wash coat on honeycomb substrate, 5 hours at 500 ℃
After firing, the catalysts 9 and 10 were fired at 1000 ° C. for 24 hours to obtain catalysts 9 and 10.
Prepared. In addition, one liter of the honeycomb substrate of the catalysts 9 and 10 was used.
The amount of coating per 100 parts by weight was 100 parts by weight.

In the combustion test, catalysts 1 to 4 were arranged at the front stage (gas inlet side) and catalysts 5 to 10 were arranged at the rear stage (gas outlet side) (catalyst length 150 mm), pressure: 3 kg / cm ² , methane:
3.5 mol% (remaining air), actual gas flow rate: 20 m / s
, The catalyst layer inlet temperature was raised at a rate of 2 ° C./min. Table 2 shows the results of measuring the temperature at which methane rapidly starts a reaction (ignition temperature) and the methane combustion rate at an inlet temperature of 400 ° C. Table 2 also shows the catalyst after the 200-hour combustion test.

[0014]

[Table 1]

[0015]

[Table 2]

(Comparative Example) In the preparation of carriers 1 to 3, immersion in an aqueous solution of palladium nitrate without addition of a rare earth element oxide, drying at 120 ° C, calcination at 500 ° C for 5 hours, The mixture was calcined for 10 hours to prepare catalyst powders 11 to 13 containing no rare earth element oxide. The catalyst powders 11 to 13 were wash-coated on a cordierite honeycomb substrate of 200 cells / inch ² and calcined at 500 ° C. for 5 hours, and calcined at 1000 ° C. for 24 hours to form a catalyst 11
~ 13 were prepared. Tables 3 show the results of the same tests as those of the examples in which the catalysts 11 to 13 were arranged in the former stage and the latter stage, or the catalysts 1 and 2 containing the rare earth element oxide were arranged only in the latter stage.

[0017]

[Table 3] As shown in Table 3, when the catalysts containing no rare earth element oxide were combined with each other, the initial activity was excellent in both the ignition temperature and the burning rate, but the activity after the 200-hour test sharply decreased. Further, even when a catalyst containing no rare earth element oxide was placed in the first stage and a catalyst containing a rare earth element oxide was added in the second stage, the activity after the 200-hour test was considerably reduced.

[0018]

As described above in detail, according to the present invention, it is possible to provide a method for stably burning a combustible gas even at a low oxidation start temperature (good ignitability) and at a high temperature.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-296423 (JP, A) JP-A-63-294411 (JP, A) JP-A-63-267803 (JP, A) JP-A 61-294803 252408 (JP, A) JP-A-63-268704 (JP, A) JP-A-61-252409 (JP, A) JP-A-61-237905 (JP, A) JP-A-5-329366 (JP, A) JP-A-5-329367 (JP, A) JP 1-56324 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) F23D 14/18 F23C 11/00 306 B01J 23 / 63 B01J 35/02

Claims (1)

(57) [Claims] 1. A carrier containing a composite oxide comprising at least two oxides of oxides of alumina, silica, titania and zirconia and a rare earth element oxide in a stage preceding the combustible gas flow path, A catalyst in which a powder supporting palladium oxide is coated on a heat-resistant base material, and a composite oxide comprising at least two oxides of oxides of alumina, silica, titania and zirconia, and a rare earth A catalyst in which powder supporting at least one oxide of magnesia, zirconia and rare earth element oxide and palladium oxide is coated on a heat-resistant substrate is disposed on a carrier containing an oxide of an element, and a flammable gas. Combusting a combustible gas.