JPS6133232A - Oxidation catalyst for catalytic combustion - Google Patents

Abstract

PURPOSE:To improve the heat resistance and activity of the titled catalyst by depositing a composite metallic oxide of perovskite structure expressed by a specified crystal structure formula on a catalyst carrier consisting of an inorganic heat-resistant material such as alumina and silica. CONSTITUTION:A composite metallic oxide having perovskite structure, expressed by the formula (A is a rere earth element such as lanthanum and praseodymium or an alkaline earth metal such as strontium and calcium, A' is cerium or strontium having a valence different from A, B is an element selected from rhodium, platinum, and ruthenium, and X stands for 0-0.2), is deposited on a catalyst carrier consisting of an inorganic heat-resistant material such as alumina and silica which is formed into a fibrous shape to prepare an oxidation catalyst for catalytic combustion. The heat resistance of the oxidation catalyst can be remarkably improved as compared with the conventional platinum catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a relatively small-sized catalytic combustion system that utilizes the heat generated from relatively light gases such as natural gas and propane gas as a heating source for homes or small-scale factories. This relates to the catalytic body of the vessel.

Structure of conventional examples and their problems In general, platinum is used as an oxidation catalyst to completely oxidize hydrocarbons into carbon dioxide and water vapor in the presence of air.

Platinum group metals such as palladium and rhodium have the highest activity. For this reason, platinum group catalysts supported on various carriers are used as oxidation catalysts. However, all of the platinum group metals have low heat resistance, and the normal temperature limit is 500°C. If used for a long time at temperatures above this temperature, thermal deterioration called sintering will occur, resulting in a decrease in activity.

For this reason, efforts have been made to add various auxiliary catalysts, improve carriers, etc., but these efforts have not produced sufficient results.

OBJECTS OF THE INVENTION An object of the present invention is to provide a highly heat resistant and highly active catalyst.

Structure of the invention v A1 mouth h-su-1 horse mackerel-=--115-French +w
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In the perovskite-type composite metal oxide represented by AI-xAxB○3, A is selected from rare earth elements such as lanthanum and praseodymium, or alkaline earth metals such as strontium and calcium, and A' is different from A from cerium and strontium. Select the one with valence B
As for the oxidation catalyst, a material selected from rhodium, platinum, and ruthenium was used as the oxidation catalyst so that the number of twists X was in the range of 0 to 0.2. As a result, the heat resistance of the melting medium has become very good, and it has become possible to use it at temperatures of 500°C or higher, which was previously impossible.

Furthermore, the activity was even higher than that of conventional catalysts.

Description of examples An embodiment of the present invention will be described below based on the drawings.

As shown in Fig. 1, the catalytic combustor main body case 1 of this embodiment
On the front side, there are an oxidation catalyst body 4 and a uniform rectifier plate 5 held by a wire mesh 2 and a rear panel 3.

Furthermore, a heater 6 for heating the catalyst body is installed between the oxidation catalyst body 4 and the uniform straightening plate 5. The oxidation catalyst is lanthanum,
Each element of cerium and rhodium has a crystal structure formula La 0.9
Ce 0. A solution of nitrate adjusted to a stoichiometric ratio to form a composite metal oxide with a perovskite structure represented by RhO2 was impregnated into a molded male shape of γ-alumina, dried, and heated at 800°C in air. The baked one was used. Next, the rear panel 3 is connected to a mixer 7, and the mixer 7 is controlled by opening and closing an air fan 8 and a gas cock 9, and a gas supply pipe 1 for supplying gas.
It is connected to 0.

Next, we will discuss its effect.

The oxidation catalyst body 4 is heated to 200 to 300° in advance with the heating heater 6.
Preheat to C. When preheating is completed, the gas that has passed through the gas supply pipe 10 and a predetermined amount of air that has been sent from the air fan 8 are mixed in the mixing pipe 7 by the action of a solenoid valve (not shown). Supplied internally. The supplied mixed gas is uniformly diffused by the uniform baffle plate 5 and then passes through the preheated oxidation catalyst body 4. At this time, the mixed gas is completely oxidized to water vapor and carbon dioxide gas. The heat generated at this time is used for heating purposes.

La Q used in the conventional platinum-based catalyst and the examples of the present invention,
9 Cs 0. The oxidation activity of methane, which is the main component of natural gas, with respect to the reaction temperature using a perovskite-type composite metal oxide catalyst having a crystal structure of I Rh03 is shown in FIGS. 2 and 3, respectively. In Figure 2, A is a fresh catalyst supporting 0.5% rhodium;
A' is obtained by firing A at 800°C for 5 hours in air. As is clear from the figure, the activity of A' is greatly reduced. On the other hand, Figure a shows LaQ, 9 used in the embodiment of the present invention.
Ce0. B is a catalyst in which <0.5% of the catalyst having a perovskite structure composed of I Rh03 is supported.

B' is obtained by firing B at 950°C for 5 hours in air. As is clear from FIG. 3, the activity of B' hardly decreased, indicating that the catalyst of the present invention has very high heat resistance. Furthermore, when comparing A and B, it is clear that the activity of the example of the present invention is high.

Effects of the Invention As described above, the oxidation catalyst composed of a composite metal oxide having a perovskite structure according to the present invention has greatly improved heat resistance compared to conventional platinum group catalysts, and can be used at high temperatures ( It is fully usable even at temperatures of 700 to 800°C. As a result, a wide catalytic combustor with a variable combustion amount can be manufactured. Furthermore, since the activity is higher than that of conventional platinum group catalysts, the amount supported can be reduced and the cost of the catalyst body can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional perspective view of a catalytic combustor according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing methane oxidation activity when using a conventional platinum-based catalyst, and Fig. 3 is a diagram showing the oxidation activity of methane according to the present invention. FIG. 3 is a characteristic diagram showing methane oxidation activity when using a catalyst having a perovskite structure in FIG. 4...Oxidation catalyst body, 6...Heating heater, 8...Air fan. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Digestion (t)

Claims (2)

[Claims] (1) In the composite metal oxide having a perovskite structure represented by the crystal structure A1-xA'xBO3, A is selected from rare earth elements such as lanthanum and praseodymium, or alkaline earth metals such as strontium and calcium, and A' For B, a material with a different valence from A was selected from cerium and strontium, and for B, one was selected from rhodium, platinum, and ruthenium so that the index x was in the range of 0 to 0.2. Oxidation catalyst for catalytic combustion. (2) The oxidation catalyst for catalytic combustion according to claim 1, wherein a fibrous inorganic heat-resistant material such as alumina or silica is used as the catalyst carrier.