JPH06159631A - Method for igniting combustion gas - Google Patents

Abstract

PURPOSE:To provide a method for igniting combustible gas through catalyst. CONSTITUTION:A method for igniting combustible gas through catalyst containing palladium therein is performed such that heat-resistant ceramics is applied as its base material, catalyst having palladium oxide carried on a carrier containing complex oxide composed of alumina, silica, titania, zirconia or these oxides and more than two kinds of oxides of at least these oxides is applied at a front stage, and further heat-resistant ceramis is applied as its base material, catalyst carried with palladium oxide and magnesium oxide thereon on a carrier containing complex oxide and rare earth element oxide of at least 2 kinds of alumina, silica, titania, zirconia or these oxides is applied at a rear stage, resulting in that the combustible gas is ignited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for burning a combustible gas such as carbon monoxide, hydrogen and hydrocarbons using a catalyst, and particularly titanium, which is the most difficult to burn, in a wide temperature range from low temperature to high temperature. The present invention relates to a catalytic combustion method capable of stable combustion.

[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 that is not generally within the range of catalyst conditions has been conventionally known. Better known. As the combustion catalyst in this conventional method, a honeycomb type ceramic such as cordierite or mullite is used as a base material, and alumina, silica, titania, zirconia alone or at least two or more oxides of these oxides are used as the base material. There has been proposed a catalyst in which a carrier containing a complex oxide composed of 1 is wash-coated and a noble metal oxide such as palladium oxide is supported as an active component.

Recently, palladium oxide is supported on a carrier containing alumina, silica, titania, zirconia alone or a composite oxide consisting of at least two or more kinds of these oxides and an oxide of a rare earth element. Catalysts have been proposed.

[0004]

However, in the combustible gas combustion method using the above-mentioned catalyst alone,
A catalyst using a carrier containing no rare earth element oxide has excellent low-temperature ignitability, but the activity of the rare earth element oxide is reduced due to aggregation of palladium oxide at 800 ° C or higher, and heat resistance. On the contrary, a catalyst using a carrier to which is added has a problem that the low temperature ignitability is poor.

In view of the above-mentioned state of the art, the present invention provides a method capable of combusting a combustible gas even at a low temperature and stably performing a complete oxidative combustion at a high temperature.

[0006]

The present invention provides a method for burning a flammable gas using a palladium-containing catalyst,
Palladium oxide was carried on a carrier containing heat-resistant ceramics as a base material and containing alumina, silica, titania, zirconia alone or a composite oxide consisting of at least two or more kinds of these oxides. A catalyst is provided in the preceding stage, and a heat-resistant ceramic is used as a base material, and alumina, silica, titania, zirconia alone or a composite oxide composed of at least two kinds of these oxides and an oxide of a rare earth element are added thereto. The carrier to contain,
A combustible gas combustion method, characterized in that a catalyst supporting palladium oxide and magnesium oxide is arranged in a subsequent stage.

The catalyst referred to in the present invention is a pellet (sphere or cylinder) or honeycomb type carrier containing 0.01% by weight to 30% by weight of palladium oxide (based on the total weight of the catalyst).
It is a supported one or a supported amount of palladium oxide and 0.01 to 20% by weight of magnesium oxide.

The term "carrier" as used herein means a heat-resistant ceramic such as mullite, cordierite, aluminum titanate, zirconia or zirconia spinel as a base material, on which alumina, silica, titania or zirconia alone or at least one of these oxides is used. 10 to 50 parts by weight of a composite oxide composed of two or more kinds of oxides per 100 parts by weight of a honeycomb-type heat-resistant ceramic substrate, and the above oxide or composite oxide for those containing an oxide of a rare earth element. The content of 1 to 20% by weight is wash-coated.

[0009]

In the method for catalytically burning combustible gas according to the present invention, alumina, silica, titania, zirconia alone or a composite oxide composed of at least two kinds of these oxides is provided in the preceding stage (gas inlet side). A catalyst containing palladium oxide as an active ingredient supported on a carrier containing a catalyst, and a catalyst containing palladium oxide and magnesium oxide supported on a carrier containing an oxide of a rare earth element in the above carrier are arranged at a later stage, so that the low temperature ignitability is good. It can be burned stably even at high temperature. Taking the combustion of methane, which is the most difficult to burn, as an example, the oxidization of methane is started at 400 ° C or lower by the catalyst of the first stage, the temperature of the catalyst layer of the first stage is controlled to be 700 ° C or less, and the catalyst of the second stage is 700-1000. Stable combustion can always be maintained by controlling the temperature range to be in the temperature range of ° C. Hereinafter, the present invention will be specifically described with reference to examples.

[0010]

【Example】

(Example 1) γ-alumina powder (particle size 60 μm, specific surface area 70 m ² / g) calcined at 1000 ° C. for 24 hours was made into a cordierite honeycomb substrate having 200 openings (200 cells) per square inch. Washcoat 50
Carrier 1 was prepared by baking at 0 ° C. for 5 hours. The coating amount of γ-alumina was 40 parts by weight per 100 parts by weight of the honeycomb substrate. Instead of γ-alumina, silica (specific surface area 78 m ² / g), titania (specific surface area 51 m ² / g),
Carriers 2 to 5 were prepared in the same manner except that zirconia (specific surface area 44 m ² / g) and silica-alumina composite oxide (specific surface area 94 m ² / g) were used. The carriers 1 to 5 were immersed in an aqueous palladium oxide solution, dried, and then calcined at 500 ° C. for 5 hours to give 10% by weight of palladium oxide (based on the total weight of the catalyst).
Supported catalysts 1-5 were prepared.

500 g of titanium tetrachloride solution is dissolved in ion-exchanged water, and ion-exchanged water is added so that pH = 3. Next, 165 g of γ-alumina is added, and after stirring for 3 hours, aqueous ammonia is added dropwise until pH = 9. After stirring for 1 hour as it is, the precipitate is filtered, washed, dried in a drier for a whole day and night, and calcined in an electric furnace at 500 ° C. for 5 hours and then at 1000 ° C. for 24 hours to obtain a titania-alumina composite oxide ( TiO ₂ : Al ₂ O ₃ = 56: 44 weight ratio) was prepared. This was wash-coated on a cordierite honeycomb base material and fired at 500 ° C. for 5 hours to obtain titania per 100 parts by weight of the cordierite honeycomb base material.
Carrier 6 containing 40 parts by weight of alumina composite oxide was prepared. The carrier 6 is dipped in an aqueous solution of palladium nitrate and dried, and then 500
A catalyst 6 supporting 10% by weight of palladium oxide (based on the total weight of the catalyst) was prepared by firing at 5 ° C. for 5 hours.

106 g of zirconium oxychloride is dissolved in ion-exchanged water, and ion-exchanged water is added so that pH = 2. Next, γ-alumina (365 g) is added, and the mixture is stirred for 3 hours, and aqueous ammonia is added dropwise until pH = 9.
After stirring for 1 hour as it is, the precipitate is filtered, washed, dried in a drier for a whole day and night, and calcined in an electric furnace at 500 ° C. for 5 hours and then at 1000 ° C. for 24 hours to obtain a zirconia-alumina composite oxide ( ZrO ₂ : Al ₂ O ₃ = 10: 90
(Weight ratio) was prepared. This was wash-coated on a cordierite honeycomb substrate and fired at 500 ° C. for 5 hours to obtain a carrier 7 of 40 parts by weight of zirconia-alumina composite oxide per 100 parts by weight of the cordierite honeycomb substrate.
The carrier 7 is immersed in an aqueous solution of palladium nitrate, dried and then 500
The mixture was calcined at 5 ° C. for 5 hours to obtain a catalyst 7 supporting 10% by weight of palladium oxide (based on the total weight of the catalyst).

(Example 2) Using the carriers 1 to 7 calcined in Example 1, they were immersed in an aqueous solution of lanthanum nitrate, cerium nitrate, neodymium nitrate or a mixed aqueous solution, and then dried at 100 ° C, 50
By firing at 0 ° C., carriers 8 to 14 containing 1 to 20 wt% of a rare earth element oxide were prepared. Carriers 8 to 14 are immersed in an aqueous solution of palladium nitrate or magnesium nitrate, dried, and then 50
What was calcined at 0 ° C. was further calcined at 1000 ° C. for 5 hours to obtain 10 wt% of palladium oxide and 1 to magnesium oxide.
Catalysts 8-14 carrying 20 wt% were prepared.

(Example 3) Catalysts 1 to 7 are arranged in the front stage (gas inlet side), catalysts 8 to 14 are arranged in the rear stage (gas outlet side), methane 3% (remainder air), gas space velocity 300,000 h.
^Under the condition of ^-1 , raise the catalyst layer inlet temperature at 2 ° C / min,
Ignition temperature and inlet temperature at which methane suddenly starts reaction 35
Table 1 shows the measurement results of the methane combustion rate at 0 ° C. and the test results after a durability (aging) test for 100 hours while maintaining the catalyst layer outlet temperature at 900 ° C.

[0015]

[Table 1]

(Comparative Example) Catalysts 1 to 7 containing no rare earth element oxide and magnesium oxide in the front and rear stages, and catalysts 8 to 14 containing rare earth element oxide and magnesium oxide in the front and rear stages. Table 2 shows the result of the arrangement and the same test as in Example 3.

[0017]

[Table 2]

When a catalyst containing no rare earth element oxide and no magnesium oxide was combined as shown in Table 2, the ignition temperature was 350 ° C. or lower, but the burning rate decreased sharply. Further, when a catalyst containing a rare earth element oxide and magnesium oxide was combined, the ignition temperature was 380 ° C. or higher, and low temperature combustion was difficult.

[0019]

As described in detail above, according to the present invention, it is possible to provide a method of completely burning a combustible gas with a low oxidation starting temperature (good ignitability) and at a high temperature.

Claims (1)

[Claims] 1. A method of burning a flammable gas using a palladium-containing catalyst, wherein a heat-resistant ceramic is used as a base material, and alumina, silica, titania, zirconia alone or at least two or more kinds of these oxides are used. In a carrier containing a complex oxide consisting of an oxide of the above, a catalyst supporting palladium oxide in the preceding stage, and a heat resistant ceramics as a base material, alumina, silica, titania, zirconia alone or these oxides Combustion of a flammable gas, characterized in that a catalyst containing palladium oxide and magnesium oxide is disposed in a subsequent stage on a carrier containing a composite oxide composed of at least two or more kinds of oxides and an oxide of a rare earth element. Method.