JPS63267804A - Oxidizing catalyst for high temperature service - Google Patents

Abstract

PURPOSE:To burn methane efficiently and also obtain the excellent heat resistance of catalysts by a method wherein catalysts of which carriers use gamma-Al2O3 and also bear palladium are placed at the early stage and catalysts of which carriers are the same as the said one and also bear noble metal are placed at the middle stage and catalysts of which carriers use specified compound oxide and also bear a kind of material at least selected from the oxide of base metal and a specified compound oxide are placed at the later stage. CONSTITUTION:As a carrier covering the surface of a honeycomb-shaped heat resisting substrate, gamma-Al2O3 is used and catalysts composed of the said carriers bearing also palladium are placed at the early stage and catalysts composed of the said carriers bearing also noble metal such as platinum, platinum-rhodium, etc., are placed at the middle stage. As a carrier, a kind of compound oxide at least selected from BaO-Al2O3, SrO-Al2O3 and CaO-Al2O3 is used and catalysts composed of the said carriers bearing also a kind of material at least selected from the oxide of base metal such as Mn, Co, Cr, Fe, etc., and a compound oxide such as LaCoO3, LaMnO3, etc., are placed at the later stage.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a high-temperature oxidation catalyst for burning gases such as carbon monoxide, hydrogen, and hydrocarbons, and in particular, the present invention relates to a high-temperature oxidation catalyst for burning gases such as carbon monoxide, hydrogen, and hydrocarbons. Methane at low temperature and high gas flow rate/
It can be oxidized with high efficiency under the conditions of low catalyst capacity ratio and low methane/air ratio, and also
The present invention relates to an oxidation catalyst that has excellent heat resistance even at high temperatures of 0°C or higher.

[Conventional technology]

The catalytic combustion method, in which combustible gases such as carbon monoxide, hydrogen, or hydrocarbons are burned in the presence of an oxidation catalyst, has been studied primarily for the purpose of purifying automobile exhaust gas, and many oxidation catalysts have been developed. The main active ingredients are oxides of noble metals such as platinum or base metals such as copper and iron, and each active ingredient is formed into granules or honeycombs, or directly onto a carrier such as alumina or titania. It is something that was carried on.

On the other hand, recently, as part of the development of low NOx combustion methods, research has been carried out on oxidation catalysts that burn propane, low calorific value gas, oil, etc. This catalyst uses honeycomb-shaped ceramics such as cordierite and mullite as a base material, and this base material has γ
-1j'203 (gamma alumina), zirconia, magnesia, α-A1203 (alpha alumina), etc. are wash coated, and pt, pt+ are added as active ingredients.
It supports oxides of noble metals such as Pd5PdSPt+Rh, or base metals such as cobalt, nickel, and manganese.

Although the conventional oxidation catalysts mentioned above show high activity against carbon oxide and propane, they have poor performance against methane, which is more stable, and their oxidation performance against methane is currently limited. Many problems remain.

In view of the above circumstances, the inventors conducted intensive research and found that a honeycomb-shaped heat-resistant base material made of cordierite, mullite, etc., can be used to catalytically oxidize methane and utilize the heat of oxidation reaction while suppressing the generation of NOx. A carrier made of zirconia or alumina is coated on the surface of the
Combining a catalyst on which d is supported and a catalyst on which a similar carrier supports an oxide of a noble metal such as platinum or platinum-rhodium, an oxide of a base metal such as nickel or cobalt, or a composite oxide such as La Co 03. It has been discovered that a highly active catalyst for methane can be obtained by
59972, Patent Application 1987-159973, Patent Application 1987-
159974, patent application No. 58-183031).

[Problem that the invention seeks to solve]

However, the catalysts that are highly active against methane as mentioned above have poor heat resistance such as 2O3, SrO-Al2O0.
No catalyst has been found that exhibits excellent heat resistance even at temperatures exceeding 0°C and 2O3, SrO-Al2O00°C. This is due to the high specific surface area (
2O3, SrO-Al2O0~2003m2/g) is often used;
When rO-Al2O exceeds 00℃, the specific surface area begins to decrease, and when it transforms to α-Al2O3 at 1200℃, the specific surface area decreases significantly to 1 m2/g or less, and due to the aggregation of the active ingredient particles dispersed on the carrier. This is because the active sites are also significantly reduced and deactivated.

The present invention was made to solve the above-mentioned problems, and has the activity of oxidizing methane from low temperatures, and moreover,
3. It is an object of the present invention to provide a high temperature oxidation catalyst having excellent heat resistance at high temperatures of 00° C. or higher.

[Means for solving problems]

The high-temperature oxidation catalyst of the present invention is an oxidation catalyst in which the surface of a honeycomb-shaped heat-resistant base material is coated with a carrier, and a plurality of stages of catalysts are combined in which an active ingredient is supported on the carrier.
! A catalyst in which palladium was supported on a carrier using γ-AJ203 was placed in the first stage, a catalyst in which noble metals such as platinum, platinum-rhodium, etc. r O-A,
At least one type of composite oxide selected from L' 203 and CaO-A Noko 03 is used, and oxides of base metals such as manganese, cobalt, chromium, and iron and L
The present invention is characterized in that a catalyst supporting at least one kind selected from complex oxides such as a, CoO3, LaMnO3, etc. is disposed at a subsequent stage.

The honeycomb-shaped heat-resistant base material used in the present invention includes ceramic base materials such as mullite, cordierite, alumina, aluminum titanate, zirconia, zirconia spinel, zircon-mullite, silicon carbide, and silicon nitride, as well as metallic base materials. Can be mentioned.

In the present invention, as the carrier coated on the surface of the honeycomb-shaped heat-resistant base material as described above, γ-A, 7-203 is used in the front stage (gas inlet side) and the middle stage. In addition, in the latter stage (gas outlet side), (B a O) o, 14 (A)
203) 0.86 (B a 06 A , i' 203
), (SrO)o, 14 (A I 203) 0.86 (
S r 0.6 A i 203), (Ca O) o,
14 (A) 203) 0.86 (Ca 0.6 A),
03) is used. These composite oxides are La-β
-Al2O3 (La, 2o3 @ lIA, il
'203, heat resistant temperature 1200℃) and 2O3, S
It has been reported that rO-Al2O does not cause sintering even above 00°C, and the heat resistance temperature of the above composite oxides is 1500 to 1600°C (surface, Vo
l, 24. NQII, I)I), 658. (
198B) ).

However, these composite oxides produce a magnetoplumbite structure when fired at about 1200°C or higher, and the specific surface area at temperatures above this temperature is lower than that of γ-A, which is often used as a carrier.
No, it's smaller than 03.

In the present invention, the active ingredients supported on each of the above-mentioned carriers coated on the surface of the honeycomb-shaped heat-resistant base material include Pd in the first stage, noble metals such as platinum or platinum-rhodium in the middle stage, and manganese and cobalt in the latter stage. Oxides of base metals and L
At least one selected from complex oxides such as aCoO3 is used. In addition to LaCoO3, the complex oxides used as active ingredients in the latter stage include LaMnO3, Lao, b S ro, a MnO3,
What is generally called a perovskite type oxide, such as Lao, 6S ro, 4CoO3, and BaCoO3, can be used.

The high-temperature oxidation catalyst of the present invention may be divided into two or more parts, for example, so as to disturb the gas flow and increase the catalytic activity. The opening may be made larger than the opening of the honeycomb.

The high temperature oxidation catalyst of the present invention can be produced, for example, by the following method. First, as a method for coating the surface of a heat-resistant base material with a carrier, a general method is to immerse the base material in a slurry solution of the carrier, wash coat it, and then bake it. In this way, Pd is added to the carrier coated on the base material.
, Pt, base metal oxides, or composite oxides such as L a M n O 3 may be supported by conventional methods. For example, P
Noble metals such as d and pt can be supported by immersing a base material coated with a carrier in an aqueous solution of chloride of these noble metals and then reducing the base material with hydrogen.

Base metal oxides can also be supported by immersing a substrate coated with a carrier in an aqueous solution of base metal salts, followed by drying and firing.

Regarding complex oxides, for example, L a M n O
In the case of 3, aqueous ammonia is added to an aqueous solution of nitrates of lanthanum (La) and manganese (M n ) to cause coprecipitation, and the precipitate is dried and fired to form a slurry of LaMnO3, which is then applied to the surface of the carrier to support the slurry. be able to.

[Effect]

During use, the oxidation catalyst has a temperature distribution such that the temperature gradually increases from the inlet to the outlet. In the high temperature oxidation catalyst of the present invention, the catalyst temperature is 2O3, SrO
-Al2O In the first and middle stages where the temperature does not exceed 00℃, γ-Al2O3 with a large specific surface area is used as a carrier, and 2O3
, SrO-Al2O Since the above-mentioned composite oxide is used as a carrier in the latter stage where the temperature exceeds or may exceed 00°C, it is advantageous for both catalytic activity and high-temperature heat resistance. However, it is difficult to say that any of the individual catalysts constituting the front stage, middle stage, or rear stage are highly active against methane when used alone. That is, the Pd catalyst at the front stage can start oxidizing methane at a relatively low temperature, but if the oxidation reaction is slow and the gas flow rate/catalyst capacity ratio (SV value) is high, methane cannot be oxidized efficiently. In the case of the middle stage PT catalyst, the oxidation reactivity is much better than the Pd catalyst, but the temperature at which oxidation starts is as high as 400°C or higher.
Generally, the temperature rises to as high as 500 to 550°C, so activity cannot be exhibited at low temperatures. In addition, a catalyst supporting a base metal oxide or a composite oxide such as L a Fvl n 03 in the latter stage has a higher temperature for starting oxidation than a PT catalyst, and is inferior to a PT catalyst in terms of reactivity. On the other hand, Cr
203, Fe203, Mn0sCoO1Cu2
Base metal catalysts such as 0 and composite oxide catalysts such as L a M n O 3 are characterized by good heat resistance.

According to the high-temperature oxidation catalyst of the present invention, an appropriate oxide is used as a carrier depending on the temperature of the catalyst, and catalysts that are difficult to use alone are combined, so that high activity against methane is achieved from low temperatures. and 2O3, SrO-Al2
Shows excellent heat resistance even at high temperatures of 000°C or higher.

Additionally, if structural improvements are made to disrupt the flow of gas, the catalytic activity can be further increased.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 A honeycomb-shaped aluminum titanate substrate with a diameter of 1 inch and 200 openings (200 cells) per square inch was wash coated with γ-Ai203,
2O3, SrO-Al2O was baked at 00°C to coat the carrier.

Catalyst A was prepared by supporting 185% by weight of palladium on this carrier.
I got it.

A honeycomb-shaped aluminum titanate substrate with a diameter of 1 inch and 400 openings (400 cells) per square inch was wash coated with γ-A, i'2 O3 and baked at 00°C with 2O3, SrO-Al2O. and coated the carrier.

Catalyst B was obtained by supporting this carrier with 1.5% by weight of platinum.

Barium aluminate (BaO 6A) is applied to a honeycomb-shaped aluminum titanate substrate with a diameter of 1 inch and 400 openings (400 cells) per square inch.
203) was wash coated and baked at 1450°C to coat the carrier. Catalyst C was obtained by supporting this carrier with 5.1% by weight of cobalt oxide.

The obtained catalyst A (length 2O3, SrO-Al2O) was placed in the front stage, catalyst B (length 1OB) in the middle stage, and catalyst C (length 26B) in the rear stage under the conditions shown in Table 1. Oxidation (combustion) of methane was carried out.

Table 1 Catalyst volume: 23.8ml! (Δ5.07 III!, B5.07m1, C13,1
71tI fuel/air ratio: 0.02kg/kg Gas ffi: 6.99m 3N/hr Gas composition: methane 3.5% by volume (the remainder is air) SV: 3000
00 (1/hr) Temperature increase rate near °C/m1n (up to holding temperature) Inlet gas holding temperature = 330 °C As a result, methane is ignited at 220 °C, and the combustion efficiency of methane at the catalyst C outlet is 9B on average, 7% , the outlet gas temperature was 1140°C on average, and the combustion was continued for 5 hours, l+u-
There was no 2 ratio.

Next, as a comparative example, catalyst C was removed from the catalyst of Example 1 and methane combustion was carried out under the same conditions as in Table 1.

As a result, the combustion efficiency at the catalyst B outlet was 85% on average.
The outlet gas temperature decreased to an average of 920''C. Even after continuing combustion for 5 hours, no change was observed in either the combustion efficiency or the outlet gas temperature.

Example 2 Strontium aluminate (Sr0.6A) 2 was applied to a honeycomb-shaped cordierite substrate with a diameter of 1 inch and 400 openings (400 cells) per square inch.
03) was wash coated and baked at 1450°C to coat the carrier. 6.8% by weight of manganese oxide in this carrier
A catalyst was obtained by supporting the catalyst.

The above catalyst A (2O3, SrO-Al2OIII) was placed in the front stage, catalyst B (2O3, SrO-Al2Om) in the middle stage, and catalyst D (28M+11) in the rear stage, and methane combustion was carried out under the conditions shown in Table 1. did.

As a result, the combustion efficiency at the catalyst outlet was 95.8 on average.
%, the average exit gas temperature was 1130°C, and there was no change even after 8 hours of continuous combustion.

Example 3 A honeycomb-shaped mullite substrate (length 38B) with a diameter of 1 inch and approximately 400 openings (400 cells) per square inch was prepared, and a portion 28M long from one end thereof was coated with barium. Wash coat aluminate, 145
After baking at 0°C, the remaining part was wash-coated with γ-Al2O3, and baked at 00°C with 2O3, SrO-Al2O to coat the carrier. 1 platinum was added to the γ-AI203 part of the carrier.
．． Lao, 6 Ca O, 4M n was supported on the barium aluminate part at 7% by weight.
Catalyst E was obtained by supporting 5.3% by weight of 03 (calcined at 1300°C). The above catalyst A (2O3, SrO-Al2
Methane combustion was performed under the conditions shown in Table 1, with OjIj placed in the front stage and catalyst E (36 m) placed in the rear stage so that the Pt catalyst was on the catalyst A side.

As a result, the combustion efficiency at the outlet of catalyst E was 94.
3%, the outlet gas temperature is 1120℃ on average, and the combustion is 5%.
There was no change even after a period of time.

Next, the catalyst E was cut to a length of 2O3, SrO-A
pt catalyst E□ of l2OM and L a g of length 28M, 6
Ca o, a M n 03 catalyst E2 was obtained. Example 1
Similarly, catalyst A is placed in the front stage, catalyst E1 is placed in the middle stage, and catalyst E2 is placed in the middle stage.
were placed in the latter stages, and methane combustion was carried out under the conditions shown in Table 1.

As a result, the combustion efficiency at the outlet of catalyst E2 was 97% on average.
, 8%, and the outlet gas temperature rose to an average of 1150'c, respectively, indicating the effect of dividing the catalyst.

Example 4 Calcium aluminate (CaO 6A
), 03) was wash coated and baked at 1450°C to coat the carrier. Catalyst F was obtained by supporting this carrier with 5.3% by weight of cobalt oxide.

The above catalyst A (IOM) is placed in the front stage, catalyst B (2O3, Sr
O-Al2O) was placed in the middle stage, and catalyst F (28 mm) was placed in the rear stage, and methane was combusted under the conditions shown in Table 1.

As a result, the combustion efficiency at the catalyst F outlet was 95.5 on average.
%, the outlet gas temperature was 1120 to 1130°C, and there was no change even after 5 hours of continuous combustion.

〔Effect of the invention〕

As described in detail above, according to the present invention, methane oxidation (combustion) can be started from a low temperature to efficiently burn methane, and moreover, 2O3, SrO-Al2O exhibits excellent heat resistance at temperatures above 00°C. It can provide an oxidation catalyst for use.

Claims (1)

[Claims] An oxidation catalyst in which the surface of a honeycomb-shaped heat-resistant base material is coated with a carrier and an active ingredient is supported on the carrier is combined in multiple stages, using γ-Al_2O_3 as the carrier and palladium on the carrier. A supported catalyst is in the first stage, a catalyst in which γ-Al_2O_3 is used as a carrier, a noble metal such as platinum or platinum-rhodium is supported on the same carrier is in the middle stage, and BaO-Al_2O_3, Sr as a carrier.
At least one type of composite oxide selected from O-Al_2O_3 and CaO-Al_2O_3 is used as a support, and oxides of base metals such as manganese, cobalt, chromium, iron, etc. and composite oxides such as LaCoO_3 and LaMnO_3 are used as the carrier. A high-temperature oxidation catalyst characterized in that a catalyst supporting at least one selected from the following is disposed at a subsequent stage.