JPS6051543A - Oxidizing catalyst - Google Patents

Abstract

PURPOSE:To contrive to enhance activity to methane and heat resistance, by combining a catalyst prepared by supporting Pd by a carrier such alumina applied to the surface of a heat resistant base material and a catalyst supporting Pt. CONSTITUTION:An oxidizing catalyst consists of a catalyst prepared by supporting Pd by a carrier (alumina or zirconia) applied to the surface of a heat resistant base material (cordierite or mullite) and a catalyst prepared by supporting Pt by the similar carrier as mentioned above. This catalyst has such a structure that the Pd-supported catalyst is arranged to a front stage and the Pt-supported catalyst to a rear stage and the whole thereof is divided into plural parts. Methane is efficiently oxidized at a low temp. by the catalyst wherein the low temp. iginition property of the Pd-catalyst and the good reactivity of Pt are combined.

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.

-The catalytic combustion method, in which hot gases such as a-carbon, hydrogen, or hydrocarbons are burned in the presence of an oxidation catalyst, has been researched primarily for the purpose of purifying automobile exhaust gas, and many oxidation catalysts have been developed. There is. The main ones are oxides of noble metals such as platinum and base metals such as copper and iron as catalyst components.
The catalyst component is formed into particles or honeycomb shapes, or directly supported on a carrier such as alumina or titania.

On the other hand, recently, as part of the development of low NO-combustion methods, oxidation catalysts for burning propane, low calorific value gas, oil, etc. have been studied. This catalyst has a honeycomb-shaped ceramic base material such as cordierite or mullite, and this base material has γ-
Wash-coat a carrier such as AA203 (gamma alumina), zirconia, magnesia, α-A7'203 (alpha alumina), and add PT, PT10P as a catalyst component.
d1Pcj, on which noble metals such as Pt+Rh or oxides such as cobalt, nickel, and manganese are supported.

Although the conventional oxidation catalysts mentioned above show high activity against -1ll-carbon and propane, they have poor performance against more stable methane, and at present, the oxidation catalysts for methane are Many problems remain in terms of performance.

In view of the above circumstances, the inventors conducted intensive research on the catalytic oxidation of methane, and as a result, the inventors conducted catalytic oxidation of methane to achieve No.
In order to utilize the heat of the oxidation reaction while suppressing the generation of Sc, phosphorus is applied onto a carrier whose surface is a heat-resistant base material such as cordierite or mullite coated with zirconia or alumina.
It was discovered that a catalyst with high methane activity and excellent heat resistance could be obtained by combining a catalyst supporting Pt with a catalyst supporting Pt on a similar support. This led to the present invention, which is unprecedented.

That is, the present invention comprises a catalyst in which palladium is supported on a support such as alumina or zirconia coated on the surface of a heat-resistant base material such as cordierite or mullite, and a catalyst in which platinum is supported on a support similar to the above. This oxidation catalyst is characterized in that the catalyst having palladium supported in the first stage is arranged and the catalyst supporting platinum is arranged in the second stage, and the whole is divided into at least two parts.

Heat-resistant base materials that can be used in the present invention include ceramics such as mullite, cordierite, alumina, zirconia, zirconia spinel, zircon-mullite, silicon carbide, and silicon nylon, as well as metallic materials. .

In addition, as carriers, γ-Ai203, α-AA203
, zirconia, magnesia, etc. can be used. A common method for coating the surface of the heat-resistant base material with such a carrier is to impregnate the base material in a slurry solution of the carrier and wash coat it. A method may also be used in which the material is immersed in water and then baked.

When preparing a catalyst by supporting Pd or pt on the carrier obtained as described above, a conventional method may be used, such as immersing the carrier in an aqueous chloride solution of pd or pt. After that, it can be prepared by hydrogen reduction.

By the way, it is difficult to say that any of the catalysts prepared as described above have high activity toward methane when used alone. That is, Pd
A catalyst can initiate methane oxidation at relatively low humidity, but if the oxidation reaction is slow and the gas flow rate/catalyst volume ratio (SV value) is high, methane cannot be oxidized efficiently. On the other hand, Pt catalysts have much better oxidation reactivity than Pd, but the temperature at which oxidation starts is as high as 400'C or higher, and generally rises to 500-550°C, making it difficult to activate them at low humidity. unable to perform.

The present invention enables a catalyst that can exhibit high activity for methane oxidation even at low temperatures by combining the features of both catalysts described above, namely, the low-temperature ignition properties of the Pd catalyst and the good reactivity of the Pt catalyst. This is what I did. Furthermore, in the present invention, by separating the two catalysts, turbulence occurs in the gas at the connecting portion, thereby further increasing the catalytic activity.

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

Example 1 A honeycomb-shaped mullite substrate (1 inch in diameter) having approximately 200 micropores per square inch was wash-coated with zirconia, and the carrier was immersed in an aqueous solution of palladium chloride and heated at 120°C. After drying for 3 hours, the temperature was further raised to 350° C. in a nitrogen stream, and while maintaining this temperature, 4% by volume of hydrogen was added to the nitrogen and fired for 2 hours while flowing, to obtain a Pd catalyst. The amount of Pd supported on the obtained Pd catalyst was 1.5% by weight. Separately, a honeycomb-shaped mullite substrate (1 inch in diameter) with 400 micropores per square inch was wash-coated with zirconia and immersed in an aqueous solution of platinum chloride, and dried at 120°C for 3 hours. After that, the temperature was raised to 400°C in a nitrogen stream, and while maintaining this temperature, 4% by volume of hydrogen was added to the nitrogen and fired for 2 hours while flowing, to obtain a Pt catalyst.Amount of Pt supported was 2.1% by weight.

In this way, PdF11 made by WA! Medium, ptyZl! Each medium was cut to a length of 23.5 mm, and Pd was added after the Pd catalyst.
By disposing and using a catalyst, methane was combusted under the conditions shown in Table 1. The results are shown in Table 2.

L catalyst volume: 23.8d SV value: 300000br ((600000br for each catalyst) Temperature increase rate near °C/min (up to holding temperature) Inlet gas holding temperature: 330°C Fuel/air ratio: 0.02Kg/ /Left gas composition: methane 3.5% by volume, remainder air Table 2 Ignition temperature (oxidation start temperature): 225°C Methane oxidation rate (at 330°C): 99.7% Output gas temperature: 1090°C By removing the Pt catalyst and using only the Pd catalyst, the gas amount remained the same (SV = 600
When methane was burned under conditions of 000hr'),
The results shown in Table 3 were obtained.

1 Ignition temperature: 223°C Methane oxidation rate (at 330°C) + 38.8% Output gas temperature: 535°C Similarly, only the PT catalyst was used, and the gas amount remained unchanged (
SV=6000001+r'), the temperature was raised at 7°C/min, oxidation started at 512'C, and when the inlet temperature was maintained at 545°C, the methane oxidation rate was 99.6%. That is, although the Pd catalyst alone starts oxidation at low humidity, the oxidation rate is insufficient, and the Pt catalyst alone cannot increase the inlet temperature and cannot obtain a high oxidation rate.

As shown in the above results, Pd catalyst is placed in the front stage and P
The present invention, in which a t-catalyst is placed in the latter stage, makes it possible for the first time to obtain a highly active oxidation catalyst for methane.

Example 2 A carrier prepared by wash-coating γ-alumina on a honeycomb-shaped cordierite substrate (1 inch in diameter) having approximately 200 micropores per square inch was immersed in an aqueous solution of barium chloride at 120°C. After drying for 3 hours, the temperature was further raised to 350°C in a nitrogen stream, and while maintaining this temperature, 4% by volume of hydrogen was added to the nitrogen solution and fired for 2 hours while flowing the P(j catalyst. The amount of Pd supported was 1.6% by weight.

The Pt catalyst prepared in Example 1 (cut into a length of 23.5 mm) was placed behind the Pd catalyst (length 23.5 mm) prepared above, and methane was oxidized and burned under the conditions shown in Table 1.

The results are shown in Table 4. ILL F Ignition temperature = 230°C Monthly methane oxidation rate (at 330°C): 99.95% Output gas temperature: 1090°C Note that the Pt catalyst is removed and only the Pd catalyst is used.

By leaving the old gas as it is (SV-) 600
00011r-") Methane was burned under the conditions in Table 1, and the results shown in Table 5 were obtained. L5L Arc ignition temperature = 228°C Q Methane oxidation rate (at 330°C): 37.2% output log gas Temperature: 520° C. The above results show that, as described in Example 1, the Pd catalyst alone does not have high activity for methane oxidation.

Example 3 A honeycomb-shaped mullite base material (1 inch in diameter, 47 mm in length) having about 200 micropores per square inch was washed with zirconia as a carrier, and 1 inch of the length of the carrier was washed with zirconia. /2 was immersed in an aqueous aqueous solution of platinum chloride, and then dried and baked in the same manner as in Example 1 to convert it into a platinum catalyst. The amount of platinum supported was 1.3% by weight. Next, the remaining part of the carrier was immersed in an aqueous solution of barium chloride, and dried and fired in the same manner as in Example 1 to convert it into a palladium catalyst.

The amount of radium supported was 1.1% by weight.

Half of the length thus obtained is the Pd catalyst, and the remaining 1 minute is the Pd catalyst.
The performance of the integrated catalyst, which is a catalyst, was measured using the materials shown in Table 1.
The results shown in Table 6 were obtained. In addition, at that time, gas was introduced from the Pd catalyst side.

L Ignition temperature: 207°C Methane oxidation rate (at 330°C): 69% Outlet gas concentration: 870°C Next, the above integrated catalyst was cut from the center to form a Pd catalyst and a PT catalyst each having a length of 23.59 mm. The catalyst performance was measured under the conditions shown in Table 1, with the Pd catalyst placed in the front stage and the Pt catalyst placed in the rear stage. As a result, the ignition temperature was 207℃,
When the inlet gas temperature was maintained at 330°C, the methane oxidation rate was 75%, and the outlet gas temperature also rose to 910°C.

From the above results, it is possible to recognize the effect of the two-part division in the present invention.

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, zirconia or alumina is added to the surface of a heat-resistant base material such as cordierite or mullite. By combining a catalyst in which Pd is supported on a support coated with Pd and a catalyst in which Pt is supported on the support, an excellent oxidation catalyst with high activity against methane and excellent heat resistance is created. This is something that can be provided.

Claims (1)

[Claims] The catalyst consists of a catalyst in which palladium is supported on a carrier such as alumina or zirconia coated on the surface of a heat-resistant base material such as cordierite or mullite, and a catalyst in which platinum is supported on the same carrier as above. An oxidation catalyst characterized in that the catalyst supported on platinum is disposed in the latter stage, and the entire catalyst is divided into at least two parts.