JPS6141610B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxidation catalyst for combustible gases such as carbon monoxide, hydrogen, and hydrocarbon gases, and the catalyst of the present invention has high durability especially when used under harsh conditions such as exhaust gas from internal combustion engines. It is a catalyst. More specifically, the present invention provides a combustible gas oxidation catalyst in which a platinum element or a base metal oxide is supported on a carrier made of cordierite or mullite coated with titania or zirconia. Exhaust gas from internal combustion engines, such as automobiles, contains large amounts of so-called polluting substances such as carbon monoxide, nitrogen oxides, and hydrocarbons, but the source of carbon monoxide in particular is automobile exhaust gas, which is found in blood. Because it combines with hemoglobin and becomes irrecoverable carboxyhemoglobin, measures to purify it have been underway for a long time. The main areas of improvement are engine improvement methods, exhaust manifold reactors, thermal reactors, and catalytic converter systems, but it is difficult to say that satisfactory results have been achieved so far. In particular, in the case of catalytic methods, oxides of noble metals such as platinum or base metals such as copper and iron are used as catalyst components, and these oxides are formed into granules or honeycomb shapes, and these catalytic component materials are used in alumina, titania, etc. There are products that are directly immersed and supported on carriers such as
These catalysts still have many problems such as performance, lifespan, and heat resistance. The present inventors catalytically oxidize combustible gases such as carbon monoxide, hydrogen, and hydrocarbon gases, such as exhaust gas from internal combustion engines and sintering furnaces, to remove harmful components and utilize the heat of oxidation reaction. In this process, a catalyst in which noble metal or base metal oxides are supported on a heat-resistant porous surface such as alumina, cordierite, or mullite coated with titania or zirconia has high performance and excellent heat resistance. Taking note of this fact, we conducted extensive experimental studies on the above-mentioned catalyst, and came to propose the present invention, which is unprecedented. Conventionally, alumina used as a carrier is about 600
It has heat resistance up to ℃ and is stable with a γ-type crystal structure, but its performance is slightly inferior to titania. Furthermore, at temperatures above 500°C, the crystal structure of titania gradually changes from an anatase type, which has catalytic activity, to a rutile type, and it has a drawback in heat resistance. Furthermore, zirconia is extremely stable thermally and has excellent performance when used as a catalyst, but it is expensive and it is not economical to mold only zirconia and use it as a carrier. Furthermore, some metal oxides used as catalytically active components melt at high temperatures or react with the carrier, reducing the catalytic activity. Therefore, the present inventors used a heat-resistant porous material such as alumina, cordierite, or muirato coated with titania or zirconia as a carrier. It was discovered that the same effect can be achieved even if the amount of titania or zirconia used is reduced. The present invention is an oxidation catalyst for combustible gases such as carbon monoxide, hydrogen, and hydrocarbon gases. This is a catalyst characterized by supporting a metal element. Here, in order to coat the surface of a cordierite or mullite base material with titania or zirconia, the respective oxides can be easily obtained by immersing the base material in an aqueous solution of titania alcoholate or zirconium nitrate and then firing. Next, a method for supporting a base metal oxide or a platinum metal element on the support thus obtained may be any conventional method. For example, when supporting a base metal oxide, a base metal nitrate aqueous solution may be used. The carrier may be immersed in a solution of chloride of a platinum metal element and then calcined, or in the case of supporting a platinum metal element, the carrier may be immersed in an aqueous solution of chloride of a platinum metal element and then reduced with hydrogen. The catalyst obtained in the above manner contains carbon monoxide,
It showed high catalytic activity in the temperature range of 300-800℃ for reactions that oxidize combustible gases such as hydrogen and hydrocarbon gases. Hereinafter, the present invention will be specifically explained with reference to Examples. Although granular catalysts are described in the examples, the shape of the catalyst is not particularly limited;
Needless to say, the catalyst may be used in a honeycomb or plate shape. Although the examples only show test results at a gas temperature of 400°C, gas temperatures other than 400°C can be used, for example from room temperature to around 1500°C. Example 1 Pellets made of γ-Al ₂ O ₃ with a particle size of 2 to 4 mm were immersed in an aqueous solution of zirconium nitrate, dried, and
After firing at ℃ for 3 hours, a carrier was obtained in which 20% by weight of zirconia was coated on alumina. The carrier thus obtained was immersed in a ferric nitrate aqueous solution, a cupric nitrate aqueous solution, and a chromium nitrate aqueous solution, respectively.
Catalysts 1, 2, and 3 were supported at 10% by weight, and catalyst 4 was prepared by immersing the same carrier in an aqueous solution of chloroplatinic acid and an aqueous solution of palladium chloride, respectively, to support platinum and palladium at 1% by weight. 5 were prepared respectively. The activity of these catalysts was evaluated under the conditions shown in Table 1, and the results are shown in Table 2.

【table】

[Table] Example 2 The γ-Al ₂ O ₃ pellets shown in Example 1 were
The carrier was immersed in an alcoholic solution of isopropyl titanate, dried, and fired at 500°C for 3 hours to obtain a carrier in which 20% by weight of titanium was supported on alumina. Catalysts 6, 7, and 8 were prepared in the same manner as in Example 1 so that iron oxide, copper oxide, and chromium oxide were supported at 10% by weight each, and platinum and palladium were each supported at 1% by weight. Catalysts 9 and 10 were prepared and the activity of the catalysts was evaluated under the conditions shown in Table 1, and the results shown in Table 3 were obtained.

[Table] Example 3 In order to see the effect of the above catalyst on the reaction of oxidizing combustible gases other than carbon monoxide, the results of evaluating the catalytic activity under the conditions shown in Table 4 using platinum catalyst 4 of Example 1 are shown below. 5.

【table】

[Table] Example 4 To test the heat resistance of an oxidation catalyst and compare it with that of a conventional catalyst preparation method, 1% by weight of platinum was added to an alumina support, a titania support, a zirconia-coated alumina support, and a titania-coated alumina support. Supported catalysts 11, 12, 4, and 9 were tested for heat resistance.
The activity of the catalyst was evaluated under the conditions shown in Table 1 by firing in air at 700°C for 120 hours, and the results shown in Table 6 were obtained.

[Table] Example 1 Particle size 2 to 4 instead of γ-Al ₂ O ₃ as carrier
Catalysts 13, 14, and 15 were prepared by supporting iron oxide, copper oxide, and chromium oxide in an amount of 10% by weight each in the same manner as in Example 1 using mmφ cordierite.
Catalysts 16 and 17 were prepared in which platinum and palladium were supported at 1% by weight, respectively. The activity of these catalysts was evaluated under the conditions shown in Table 1, and the results are shown in Table 7.

[Table] Catalyst 16 was calcined in air at 700°C for 120 hours and the activity of the catalyst was evaluated under the conditions shown in Table 1.
The same result as before the heat resistance test was obtained, with an oxidation rate of 94%. Example 2 Particle size 2 to 4 instead of γ-Al ₂ O ₃ as carrier
Catalysts 18, 19, and 20 were prepared by using mmφ mullite to support iron oxide, copper oxide, and chromium oxide in an amount of 10% by weight, respectively, in the same manner as in Example 1.
Catalysts 21 and 22 each containing 1% by weight of palladium were prepared. The activity of these catalysts was evaluated under the conditions shown in Table 1, and the results are shown in Table 8.

[Table] Catalyst 21 was calcined in air at 100°C for 120 hours and the activity of the catalyst was evaluated under the conditions shown in Table 1.
The same result as before the heat resistance test was obtained, with an oxidation rate of 93%.

Claims (1)

[Claims] 1. Oxidation of flammable gas characterized by supporting cordierite or mullite with oxides of platinum metal elements or base metals such as copper, chromium, iron, nickel, and cobalt on a carrier to which titania or zirconia is added. catalyst.