JPH04135640A - Oxidation catalyst - Google Patents

Abstract

PURPOSE:To obtain an oxidation catalyst excellent in heat resistance which is hardly sintered even at a high temp. by using a lanthanum manganite perovskite-type oxide of specified compsn. CONSTITUTION:A lanthanum manganite perovskite-type oxide expressed by La1-xAxMn1-alphaO3 (wherein 1<=x<=0.6, A is one or more kinds of elements selected from Ca, Sr and Ba, and alpha>0) is used as the oxidation catalyst for the combustion of gas such as hydrogen, carbon monoxide and hydrocarbon. This oxidation catalyst is prepared by compounding a small amt. of Mn2O3 and then calcined to cause Mn shortage. Thereby, the obtd. catalyst is excellent in heat resistance and is hardly sintered even at a high temp.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an oxidation catalyst, for example, an oxidation catalyst for burning gases such as hydrogen, carbon oxide, hydrocarbons, etc. Methane, which is difficult to oxidize, at low temperature,
The present invention relates to an oxidation catalyst that can perform oxidation with high efficiency under conditions of a high gas flow rate/catalyst volume ratio and has excellent heat resistance even at high temperatures of 1000° 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 honeycomb shapes, or directly supported on a carrier such as alumina or titania. This is what I did.

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 uses honeycomb-shaped ceramics such as cordierite or mullite as a base material, and this base material has r
A120s (gamma alumina) Zirconia, Magnesia, α-^120! (alpha alumina), etc., and Pt, P as active ingredients.
t+Pd.

It supports oxides of noble metals such as Pd, Pt+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.

Recently, as a catalyst that is heat resistant even at around 1000 degrees Celsius, a catalyst in which a catalytically active component is supported on a carrier mainly composed of a composite oxide of aluminum and lanthanum (Japanese Unexamined Patent Application Publication No. 1989-1999-1) has been developed.
12132) or a catalyst whose main component is a composite oxide of an alkaline earth metal element and aluminum (Japanese Unexamined Patent Publication No. 12132-
153158) and the like have been proposed.

[Problem to be solved by the invention]

When conventional catalysts are used at temperatures above 1000° C., the carrier or catalytic active components are sintered by heat, resulting in a rapid decrease in activity, making them practically unusable.

In view of the above-mentioned state of the art, the present invention aims to provide an oxidation catalyst with excellent heat resistance that is resistant to sintering even at high temperatures.

[Means to solve the problem]

The present invention provides (1) Lad-xAxMn1-g [+3 (0
≦x≦0.6, A: Ca.

An oxidation catalyst comprising a lanthanum manganite perovskite oxide represented by one or more of Sr and Ba (α>0).

(2) Cordierite, mullite or MgO, Al
An oxidation catalyst comprising a honeycomb-shaped heat-resistant base material selected from crystalline composite oxides consisting of 2O3°TlO2 and coated with the lanthanum manganite perovskite oxide of item (1) above.

It is.

Perovskite type oxide is represented by ABO3 (A, Blt metal element). For example, in the case of LaMnO3, L
a is called mullite, an MnB site element. Conventional △ perovskite type oxides, for example, in lanthanum manganite type (La-Mn type), a part of La in mullite is replaced with Ca,
Lad-xAJn03 compositions substituted with Sr or Ba are often used.

The present inventors completed the present invention by discovering that sintering due to heat can be prevented by creating Mn defects in a lanthanum manganite-based perovskite oxide, and that it has excellent oxidation activity even at high temperatures. be.

[Effect]

Lad-xAJr++ -cx 03 according to the present invention
A lanthanum manganite-based perovskite oxide expressed by (0≦x≦0.6, A: one or more of Ca, Sr, Ba, α>0) is a lanthanum manganite-based perovskite oxide that resists sintering due to heat by creating Mn defects. It is manufactured by the following method.

(2) La compound, [a and/or Sr and/or Ba compound, and Mn compound are blended and calcined so that the composition becomes Lad-xAxMr++-αO3.

■ In addition to blending a La compound, Ca, Sr and/or Ba compound, and Mn compound to obtain the composition of Lad-xAJno3, a small amount of Ca and/or Sr is added.
and/or a Ba compound and calcined.

In addition, the above-mentioned crystalline composite oxide consisting of MgO, Al2O3, and TiOz includes magnesia, magnesium carbonate,
A mixture of Mg compounds such as magnesium hydroxide, alumina, AI compounds such as aluminum hydroxide, and Ti compounds such as anatase or rutile titanium oxide,
It means a low-expansion product obtained by crystallizing by firing at 1300 to 1700°C.

Lad-XAxMnO+ (0≦x≦0.6, A=C
a and/or Sr and/or Ba) is, for example, La2O
3, CaCO3 and/or 5rCOs and/or BaC
It is manufactured by blending O3 and Mn2L so that each element has the target composition and calcination, but the calcination temperature is set to 13
If the temperature is 50°C, the calcined product becomes solidified in the crucible. However, Lad−++AxMn+−αo3(α
> 0), a calcined product can be obtained without caking at all.

Furthermore, La2D, , CaCO3 and Mn2O3 are
In accordance with the composition of a + -X Ca x Mn03, La20a, 5rCO+ and Mn2O3 were also added to L
If they are mixed according to the composition of a+-xsrJnlL, and a trace amount of Ban is added to each of these and calcined, a calcined product can be obtained without caking. The same effect can be obtained even if CaCL or 5rCL is added in excess.

Cordierite, mullite or MgO, Al2O3゜T
As a method for supporting the above-mentioned lanthanum manganite perovskite type oxide on a honeycomb-shaped heat-resistant base material selected from crystalline composite oxides consisting of 1O2, the support is immersed in a slurry of perovskite type composite oxide powder. This is generally done by washcoating at a temperature of 500°C or higher and baking at a temperature of 500°C or higher.

The catalyst of the present invention is used for catalytic combustion of hydrocarbon gases such as hydrogen, carbon oxide, and methane, and combustible gases such as oxygen-containing compounds, at a temperature of 100 to 1400°C, gas superficial velocity (G
H3V) used under conditions of 102 to 106h-'.

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

[Example 1] Powders of LaJ3.5rCL, CaCO3 and Mn2O3 were mixed as raw materials in the proportions shown in Table 1, and heated at 1350°C.
Calcining was performed for 5 hours to obtain catalysts 1 to 4 of lanthanum manganite-based perovskite oxides of the Mn-deficient type having the compositions shown in Table 1, and a comparative catalyst without Mn deficiency as a comparative catalyst.

The activity of these catalysts was evaluated using a gas containing 1% methane (the balance being air) at a superficial gas velocity of 100,000 h and a reaction temperature of 1000°C. Activity evaluation test 10 hours and 1000
The conversion rate after time is shown in Table 1.

Table [Example 2] 0.88g of SrCO3 (
Catalyst 5) or 0.6 g of CaCO3 (catalyst 6) or B
0.91 g of aO (catalyst 7) was added and calcined at 1350° C. for 5 hours to obtain Mn-deficient lanthanum manganite perovskite oxide catalysts 5 to 7.

These catalysts were tested in the same manner as in Example 1, and the results are shown in Table 2.

Table 2 [Example 3] SrCO3, [:aCDs, BaC0+, a (DH)3 and MnJ3 powders were mixed as raw materials in a predetermined ratio and calcined at 1000°C for 24 hours. , Mn-deficient lanthanum manganite perovskite oxide catalyst 8 with the composition shown in Table 3
I got 12.

These catalysts were tested in the same manner as in Example 1, and the results are shown in Table 3.

Table 3 [Example 4] Activity evaluation test using catalyst 10 of Example 3 using air containing hydrogen, -carbon oxide, methanol or propane as a raw material at a reaction temperature of 300°C and a superficial gas velocity of 1000h-' As a result, the conversion rate was 100 for all raw materials.
%Met.

[Example 5] 200 openings per square inch with a diameter of 1 inch (
Honeycomb-like cordierite (200 cells) with
MgO・2AI203・5SI02) base material or MgO,
Using a crystalline composite oxide (MgD・4A1203・6TiO−) base material consisting of A12[]3 and TiO2, the powder of catalyst 10 of Example 3 was wash coated on the base material, and baked at 1200°C to form the base material. A catalyst 20.21 coated with 20 parts by weight of catalyst 10 per 100 parts by weight was obtained.

The activity of these catalysts was evaluated using air containing 1% methane at a superficial gas velocity of 200,000 h-' and a gas temperature at the inlet of the catalyst layer of 700 DEG C. The results are shown in Table 5. Table 5 shows 1000
The results after the time activity evaluation test are also listed.

Table 5 [Effects of the Invention] As detailed above, according to the present invention, an oxidation catalyst with high activity and excellent heat resistance can be provided.

Akira

Claims (2)

[Claims] (1) La_1_-_xA_xMn_1_-_αO_3
(0≦x≦0.6, A: one or more of Ca, Sr, Ba,
An oxidation catalyst comprising a lanthanum manganite perovskite oxide represented by α>0). (2) Cordierite, mullite or MgO, Al_2
A honeycomb-shaped heat-resistant base material selected from crystalline composite oxides consisting of O_3 and TiO_2 is
An oxidation catalyst characterized by being coated with the lanthanum manganite perovskite oxide of item 1).