JPS6054736A - Oxidation catalyst - Google Patents

Abstract

PURPOSE:To improve activity and heat resistance of catalyst by using catalyst supporting Pd on a carrier coated on a honeycomb base material in combination with catalyst supporting base metal oxide, etc. on the similar carrier and by changing the aperture of the base material. CONSTITUTION:In the oxidation catalyst of this invention, the catalyst A is arranged to the front stage of the honeycomb, and >= one kind of the catalyst group B are arranged to the rear stage of the honeycomb, and the aperture of the front stage honeycomb is made larger than the aperture of the rear stage honeycomb. The catalyst A comprises Pd supported on a carrier such as alumina or zirconia coated on the surface of honeycomb-shaped heat resistant base material such as cordierite, mullite, etc. The catalyst group B is prepd. by supporting noble metals such as Pt, Pt-Rh, oxide of base metal such as Ni or Co, or compound oxide such as LaCoO3, etc. on a carrier similar to the above-described carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxidation catalyst for burning gases such as carbon monoxide, hydrogen, and hydrocarbons, and in particular, methane, which is the least oxidizable of various heat-generating gases, can be oxidized at low temperatures and at high temperatures. The present invention relates to an oxidation catalyst that can oxidize with high efficiency under conditions of a low flow rate/catalyst capacity ratio and a low methane/air ratio.

BACKGROUND OF THE INVENTION Catalytic combustion methods, in which hot gases such as carbon monoxide, hydrogen, or hydrocarbons are combusted in the presence of an oxidation catalyst, have been studied primarily for the purpose of purifying automobile exhaust gas, and many oxidation catalysts have been developed. The main catalyst components are oxides of noble metals such as platinum or base metals such as copper and iron, and the catalyst components are formed into granules or honeycomb shapes, or directly onto a carrier such as alumina or titania. It is something that has been carried over.

On the other hand, recently, as part of the development of low NOx combustion methods, oxidation catalysts for burning propane, low calorific value gas, oil, etc. have been researched. This catalyst has a ceramic base material such as honeycomb-type cordierite or Murai 1~, and this base material has γ
- 20g of AI (gamma alumina), zirconia, magnesia, α-A+20s (alpha alumina), etc. is coated with a support such as Pt, Pt+P as a catalyst component.
Noble metals such as d, Pd, Pt+Rh, or copal [-
, nickel, manganese, and other oxides.

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

In view of the above circumstances, the inventors conducted intensive research on catalytic oxidation of methane and found that methane was catalytically oxidized to produce NO.
In order to utilize the heat of oxidation reaction while suppressing the generation of A catalyst in which 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 LaCOO,+ is supported on a carrier is combined, and in both catalysts, the honeycomb-shaped base material is It was discovered that a catalyst with high activity against methane and excellent heat resistance can be obtained by changing the opening size, and based on this discovery, the present invention, which is unique in its own right, was developed.

That is, the present invention provides a catalyst in which palladium is supported on a carrier such as alumina or zirconia coated on the surface of a honeycomb-shaped heat-resistant base material such as Cordurai]. One or more catalysts selected from catalyst group B, in which noble metals such as platinum or platinum-rhodium, oxides of base metals such as nickel and cobalt, or composite oxides such as Lacoos, are supported on a similar carrier are used in the subsequent stage. This oxidation catalyst is characterized in that the whole is divided into at least two parts, and the opening of the honeycomb in the rear stage catalyst is smaller than the opening of the honeycomb in the front stage catalyst A.

Examples of the honeycomb-shaped heat-resistant base material that can be used in the present invention include ceramics such as mullite, cordierite, alumina, zirconia, zirconia spinel, zircon-mullite, silicon carbide, and silicon nitride, as well as metallic materials.

In addition, as carriers, γ-A12o3, α-he1□O8,
Zirconia, magnesia, etc. can be used. One method of coating the surface of the heat-resistant base material with such a carrier is generally to impregnate the base material in a slurry solution of the carrier and wash it. A method may also be used in which the material is immersed in an aqueous solution and then fired.

Pd5Pt on the carrier obtained as above.

When preparing a catalyst by supporting an active substance such as a base metal oxide or a composite oxide such as L a COOs, a conventional method may be used. For example, noble metal catalysts such as Pd and P't can be prepared by immersing a carrier in an aqueous chloride solution of these noble metals and then reducing the catalyst with hydrogen. Base metal catalysts can also be prepared by immersing a support in an aqueous solution of base metal salts, followed by drying and calcining. Regarding composite oxide catalysts, for example, in the case of LaCOOs, aqueous ammonia is added to an aqueous solution of nitrates of lanthanum ([a) and cobalt (Co) for coprecipitation, and the precipitate is dried and calcined to form a slurry of LaCOO. It can be prepared by applying it to the carrier.

By the way, none of the catalysts prepared as described above can be said to have high activity against methane when used alone. That is, Pd
Methane oxidation can be initiated at relatively low temperatures on catalysts, but
If the oxidation reaction is slow and the gas flow rate/catalyst capacity ratio (SV value) is high, methane cannot be oxidized efficiently. On the other hand, in the case of catalyst group B, for example, the Pt catalyst has good oxidation reactivity as well as the Pd catalyst, but the temperature at which oxidation starts is as high as 400°C or higher, and generally 500°C or higher.
Since the temperature rises to as high as 550°C, it cannot exhibit activity even at low temperatures. In addition, catalysts supporting base metal oxides and composite oxides such as L a COOs have higher oxidation temperatures than Pt catalysts, and are inferior to Pt catalysts in reactivity. However, CrtOs, Fe2O3, Fe
50. , Nio.

Base metal catalysts such as coo, Cu 20, and L a COO
Composite oxide catalysts such as s have a feature of good heat resistance.

The present invention has made it possible to create an oxidation catalyst with high activity for methane by combining catalysts that are difficult to use alone as described above and adding structural elements to increase the catalytic activity. . That is, in the present invention, the catalyst is divided, and by changing the opening of the honeycomb-shaped base material in each stage of the catalyst, turbulence is generated in the gas at the connecting portion, and the catalytic activity is further enhanced.

In addition, as the composite oxide in the present invention, LaC0O
In addition to s, LaMjlOs, Lao, 7p
bo, 5MnOs% Lao, 5Sro, 1Mn03
, Lao, oS ro, +M n O,, B a CO
What is generally called a nihefroskite type oxide, such as O3, can be used.

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

Example 1 Pd was applied to a carrier obtained by wash-coating zirconia on a honeycomb-shaped mullite substrate (1 inch in diameter, 9 rrm in length) having approximately 200 micropores per square inch.
．． Catalyst A supported at 5% by weight and 40% by weight per square inch.
Honeycomb-shaped Murai 1 with 0 micropores - Catalyst B in which 1.5% by weight of Pd was supported on a carrier prepared by wash-coating zirconia on a base material (-1 inch in diameter) and 4°0 per square inch. A honeycomb-shaped mullite base material (1 inch in diameter) having 1 inch of micropores was prepared with catalyst C in which 2.1% by weight of Pt was supported on a carrier made by wet-coating zirconia, and from these catalysts A, B, and C, A combinatorial catalyst engineering, such as ■, was obtained.

Catalyst T: Catalyst A (length 23.5m) in the front stage + Catalyst C (length 23.5m) in the rear stage Catalyst ■: Catalyst B (length 23.5#) in the front stage + Touch in the rear stage!
11C (length 23.5 m>Methane oxidative combustion was carried out under the conditions shown in Table 1 for the above combination catalysts ① and ②.

The results are shown in Table 2.

L upper catalyst volume: 23.8me (11.9d+11.9d) Gas amount: 7.14m3N/hr SV value: 300000hr" Temperature increase rate = 7℃/min (up to holding temperature) Inlet gas holding temperature: 330℃ Fuel/ Air ratio: 0.021 (g/lτ) and gas composition: methane 3.5% by volume, the remainder being air i2 Ignition temperature Methane oxidation rate Catalyst I: 225°C 99.7% Catalyst N: 270°C 95.6% This result As shown in Figure 2, the catalyst according to the structure of the present invention has a lower ignition temperature than the catalyst (2) in which the mesh size of the honeycomb-shaped base material is reversed, and the methane oxidation rate when the inlet temperature is maintained at 330°C. Therefore, catalyst ■ is clearly superior to catalyst ■.

Example 2 A catalyst was prepared in which 7.8% by weight of cobalt oxide was supported on a carrier obtained by wash-coating zirconia on a honeycomb-shaped mullite base material (1 inch in diameter) having about 400 micropores per square inch, and By combining this catalyst with catalysts A, B, and C prepared in Example 1, the following combination catalyst 111. I got an IV.

Catalyst ■: Catalyst A (length 9 trvn) in the front stage + Catalyst C (length 5 m) in the middle stage Catalyst D (length 4 mm) in the rear stage Catalyst Iv: Catalyst B (length 9 mm) in the front stage + Middle stage Touch t1. C (length 5#) Catalyst D (length 4 mm) in the rear stage of the cow This combined catalyst 111. When methane was burned using IV under the conditions shown in Table 3, the results shown in Table 4 were obtained.

L support catalyst volume: 9.1me (4.6m+2.5m+2.0m) Gas I: 2
．． 73m" N/hr SV value: 300000hr-' Temperature rising rate = 7℃/min (holding) up to 3 degrees) Inlet gas holding temperature: 330℃ Fuel/air ratio + 0, 0.2 Kg/9 Gas composition: Methane 3 .5% by volume, the remainder is air A Ignition temperature Methane oxidation rate Catalyst m: 235°C 99.2% Catalyst IV: 275°C 87.3% From the above results, the performance of catalyst ① according to the configuration of the present invention is as follows:
It is clearly superior to Catalyst IV, which is different from the present invention, in terms of the opening of the catalyst in each stage.

Example 3 A honeycomb-shaped cordierite substrate (1 inch in diameter) having about 200 micropores per square inch was wash-coated with γ-alumina to form a carrier, and 1.0 mm of Pd was applied to the carrier.
Catalyst E with 6% by weight supported was prepared. In addition, a honeycomb-shaped cordierite base material (1 inch in diameter) having approximately 400 micropores per square inch was wash-coated with γ-alumina to form a carrier, and 1.6% by weight of Pd was added to the carrier.
A supported catalyst F was prepared. Next, this catalyst E.

F was combined with catalysts C and D prepared in Example 2 to obtain the following combination catalysts V and VI.

Catalyst V: Catalyst E in the front stage (length 9 mm>+Catalyst C in the middle stage)
(In order of length 5) + Catalyst D in the rear stage (length 4 #) Catalyst ■2 Catalyst F in the front stage (length 9 #) + Catalyst C in the middle stage (length 5 #) + Catalyst D in the rear stage (length 4 m) When methane was combusted using the above combination catalysts v and vi under the same conditions as shown in Table 3 above, the results shown in Table 5 were obtained.

5 Ignition temperature Methane oxidation rate Catalyst V: 228°C 99.3% Catalyst VI: 250°C 92.4% In this case as well, the performance of catalyst V according to the configuration of the present invention is lower than that of catalyst Vl contrary to the present invention. clearly superior.

As detailed above, according to the present invention, when catalytically oxidizing methane and utilizing the heat of oxidation reaction while suppressing the generation of NOx, the surface of a honeycomb-shaped heat-resistant base material such as cordierite or Murai 1 is used. A catalyst in which Pd is supported on a zirconia or alumina support coated with Pd, and an oxide of a noble metal such as platinum or platinum-rhodium, a base metal oxide such as nickel or cobalt, or a composite oxide such as LaCoO3 is supported on the same support. By combining these catalysts and changing the opening of the honeycomb-shaped base material in both catalysts, it is possible to provide an excellent oxidation catalyst that is highly active for methane and has excellent heat resistance, and is unparalleled. It is.

Applicant Sub-Agent Patent Attorney Takehiko Suzue Continued from page 1 @ Inventor Norihisa Miyako ± 1 0 Inventor Suwa Witness No. η, 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Research Center

Claims (1)

[Claims] Catalyst A, in which palladium is supported on a carrier such as alumina or zirconia coated on the surface of a honeycomb-shaped heat-resistant base material such as cordierite or mullite, is placed at the front stage, and platinum, platinum-rhodium, etc. are supported on the same carrier as above. 1 selected from catalyst group B supporting noble metals, oxides of base metals such as nickel and cobalt, or composite oxides such as LaC0Os.
The species or two or more species are arranged in the latter stage, and the whole is at least two species.
An oxidation catalyst characterized in that it is divided and the opening of the honeycomb in the rear catalyst is smaller than the opening of the honeycomb in the catalyst A of the front stage.