JPH07246339A - Low-temperature oxidation catalyst - Google Patents

Abstract

PURPOSE:To obtain a low-temp. oxidation catalyst using oxides of base metals, capable of selectively oxidizing CO at a low temp., e.g. at <=100 deg.C and having durability. CONSTITUTION:Fluororesin is added by 5-50wt.% to a metal oxide mixture essentially consisting of manganese dioxide and cupric oxide and they are heated at 300-400 deg.C to obtain the objective low-temp. oxidation catalyst. The metal oxide mixture may be prepd. by blending manganese dioxide and cupric oxide with 5-15wt.% silver oxide or nickel oxide. When such catalytic components are carried on a carrier having a large surface area such as active carbon, the resultant catalyst can be allowed to more effectively exhibit its catalytic function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation catalyst that oxidizes harmful components such as gas to convert them into harmless components. More specifically, the present invention relates to an oxidation catalyst that selectively oxidizes carbon monoxide at relatively low temperatures. It relates to a low temperature oxidation catalyst which is converted to carbon.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for oxidizing carbon monoxide, platinum (Pt), palladium (P
d), rhodium (Rh), etc. are known, and in oxides of base metals, manganese dioxide (MnO ₂ ) and cupric oxide (Cu).
O), silver oxide (Ag ₂ O), nickel oxide (NiO),
A single oxide such as cobalt oxide (CoO) or a mixture of these oxides is known.

Of these oxidation catalysts, those of the noble metal type function at a relatively high temperature (for example, 100 ° C. or higher) and have no selectivity for the oxidation of carbon monoxide, but rather in the presence of hydrogen (H ₂ ). In the oxidation at 1, there is a tendency to promote the oxidation of hydrogen rather than carbon monoxide. On the other hand, some oxide-based catalysts function well even at relatively low temperatures (100 ° C or lower, for example, room temperature), and catalysts that selectively oxidize carbon monoxide even in the presence of hydrogen are known. Has been.

[0004]

The catalysts that work at low temperatures such as room temperature as described above have been conventionally used as gas masks for removing carbon monoxide, but their catalytic function is remarkably deteriorated by moisture in the atmosphere. Therefore, it could not be used for a long time. That is, noble metal-based oxidation catalysts that function at high temperatures are less susceptible to the effects of water vapor and the like, but there is a problem that not only heating is required but also carbon monoxide alone cannot be selectively oxidized. Such an oxide-based catalyst that functions at a relatively low temperature has a problem that durability is poor and stable high performance cannot be maintained for a long time.

The present invention has been made in order to solve these problems, and uses a base metal-based oxide to selectively oxidize carbon monoxide at low temperature and has a durable low temperature. It is intended to provide an oxidation catalyst.

[0006]

The low temperature oxidation catalyst of the present invention comprises manganese dioxide (MnO ₂ ) and cupric oxide (Cu).
It is characterized in that a fluororesin is added to a mixture of metal oxides containing O) as a main component in a proportion of 5 to 50% by weight and heat-treated at a temperature of 300 to 400 ° C. Further, it is characterized in that such a catalyst component is supported on a large surface area carrier.

In the present invention, examples of the fluororesin include polytetrafluoroethylene, polytrifluorochloroethylene and the like, and the use of polytetrafluoroethylene is particularly preferable.

In the present invention, such a fluororesin is added to the mixture of the base metal oxides described above, and the mixture is heated at a temperature of 300 to 400 ° C. which is higher than the softening temperature of the fluororesin to form mixed oxide particles. The surface is covered with a fluororesin, and the deterioration of the catalytic function due to moisture is suppressed. That is, the mixture of manganese dioxide and cupric oxide has a catalytic function of selectively oxidizing carbon monoxide, but the function is remarkably deteriorated by water, so that stable performance cannot be maintained for a long time. Therefore, by adding a fluororesin to the mixture of the above-mentioned oxides, heating the mixture, and coating the surface of the oxide particles with the melt-softened fluororesin, water repellency is imparted, and the deterioration of the function is prevented. Further, such surface treatment with a fluororesin prevents the wetting of the oxide particles due to the condensation of water vapor at a low temperature of 100 ° C. or less, for example, and stable and high performance is maintained for a long time.

The amount of the fluororesin added is 5 to 50% by weight with respect to the mixture of base metal oxides. If the addition ratio of the fluororesin is more than 50% by weight, a highly active catalyst cannot be obtained. On the other hand, if it is less than 5% by weight, the effect of the addition is not exerted and the catalyst life deteriorates. It is not preferable because it shortens. A more desirable amount to add is 20 to 30% by weight based on the mixture of oxides.

In the present invention, silver oxide (Ag ₂ O) or nickel oxide (NiO) is added to the mixture of manganese dioxide and cupric oxide in an amount of 5 to 15% by weight of the total oxide. It can be blended. When silver oxide or nickel oxide is mixed in such a ratio, there is an advantage that a catalyst having higher activity can be obtained. Furthermore, by supporting a mixture of these oxides, which are catalyst components, on a carrier having an extremely large surface area, it is possible to more effectively exhibit the catalytic function.
Here, examples of the carrier having a large surface area include activated carbon and alumina. For alumina, the use of γ-alumina is preferred, but the use of hydrophobic activated carbon is most preferred. Among activated carbons, it is desirable to use carbon black or acetylene black which is stable during heat treatment in air.

The low temperature oxidation catalyst of the present invention is prepared by a wet method.
For example, it is prepared as shown below. That is, the active manganese dioxide precipitate obtained by the wet method is heated to 150 ° C. in oxygen and dried, and then suspended in a solution containing a predetermined amount of copper nitrate and, if necessary, silver nitrate or nickel nitrate. It is made turbid, then sodium carbonate is added thereto to precipitate a carbonate, and the precipitate is dried by heating in air at 150 ° C. Next, this dried product was suspended in pure water, and a predetermined amount of a commercially available dispersion of polytetrafluoroethylene (dispersion liquid) was added to the suspension and well stirred, and then a floc forming agent was added. Filter. Then, the filtered product is dried and heat-treated at 300 to 380 ° C., and then the processed product is pulverized into granules.

Further, in order to obtain the catalyst supported on the carrier,
When manganese dioxide is prepared by the wet method, a predetermined amount of carrier is added to impregnate or coprecipitate, and the coprecipitate is used to prepare by the same procedure.

[0013]

In the low temperature oxidation catalyst of the present invention, a fluororesin such as polytetrafluoroethylene is added at a predetermined ratio to a mixture of manganese dioxide and a base metal oxide containing cupric oxide as a main component, followed by heat treatment. Has been done,
The surface of the particles of the oxide is covered with a fluororesin to impart water repellency. Therefore, moisture in the atmosphere does not adhere to the oxide surface to deteriorate the catalytic function, and stable and high performance is maintained for a long time. Further, when the catalyst component thus surface-treated with the fluororesin is supported on a carrier having a large surface area such as hydrophobic activated carbon, the function is more effectively exhibited and the performance as a catalyst is improved. Is improved.

[0014]

EXAMPLES Next, examples of the present invention will be described. The low temperature oxidation catalyst of the present invention is not limited to the above examples. Examples 1 to 5 Granular catalysts were prepared by the above-mentioned method using a mixture of base metal oxides having the composition shown in Table 1, polytetrafluoroethylene, and a carrier material. As a comparative example, without adding polytetrafluoroethylene,
A catalyst was prepared in the same manner as in the examples using only the mixture of base metal oxides.

Then, an activity test was conducted on each of the obtained catalysts to determine the initial activity and the activity after 24 hours. The test results are shown in the lower column of Table 1. Incidentally, the catalyst activity test, using a normal flow type reaction apparatus, as a processing gas.
To a cylinder gas (nitrogen 79.8%, oxygen 20%) containing 1 %% carbon monoxide and 0.1 %% hydrogen, saturated steam pressure steam at the inlet gas temperature was added, reaction temperature 30 ° C, reaction pressure 0.5 kgG / c
m ^2, and carried out under the conditions of a space velocity 3500~5000H ^-1. And
The conversion rate of carbon monoxide to carbon dioxide was determined from the gas analysis results, and this was taken as the catalytic activity.

[0016]

[Table 1]

From the test results shown in Table 1, the catalysts of Examples have an initial activity as a catalyst for the oxidation of carbon monoxide that is not necessarily higher than that of the conventional catalyst (Comparative Example), but the activity of the catalysts is still high even after 24 hours. It was found that the durability did not decrease and the durability was significantly improved. It was also found that when a catalyst is supported on a carrier having a large surface area such as alumina or carbon black, high activity can be obtained even if the amount of expensive silver oxide is small. Examples 6 to 9 Polytetrafluoroethylene was added to the mixture of base metal oxides having the same composition as in Example 3 in different proportions as shown in Table 2 to prepare catalysts in the same manner. Next, the catalysts obtained in Examples 6 to 9 were subjected to the same catalytic activity test as in the above Examples to determine the activity. The test results are shown in the lower column of Table 2.

[0018]

[Table 2]

From the test results shown in Table 2, when the amount of polytetrafluoroethylene added is increased, the catalytic activity is decreased, and when it is decreased, the durability as a catalyst is decreased, but the amount added is relative to the base metal oxide mixture. 5 to 50% by weight, a sufficiently high initial activity was obtained and the high activity was 24%.
It was found to be well maintained after hours.

[0020]

As described above, in the low temperature oxidation catalyst of the present invention, the surface of the particles of the base metal oxide, which is the catalyst component, is coated with the fluororesin, and the water repellency is imparted.
Deterioration of the catalytic function due to moisture is unlikely to occur, and stable and high performance is exhibited for a long time. Further, by supporting such a catalyst component on the large surface area carrier, the function is more effectively exhibited. Therefore, it is possible to reduce the use of expensive catalyst components and improve the economical efficiency.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical location C01B 31/20 A (72) Inventor Naoki Yamada 2-4 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Keihin Office

Claims (5)

[Claims] 1. A fluororesin is added at a rate of 5 to 50% by weight to a mixture of manganese dioxide (MnO ₂ ) and a metal oxide containing cupric oxide (CuO) as a main component at 300 to 400 ° C.
A low-temperature oxidation catalyst characterized by being heat-treated at the temperature of. 2. The mixture of metal oxides is a mixture of manganese dioxide and cupric oxide mixed with silver oxide (Ag ₂ O) or nickel oxide (NiO) in a proportion of 5 to 15% by weight. The low temperature oxidation catalyst according to claim 1. 3. A mixture of manganese dioxide and a metal oxide containing cupric oxide as a main component and 5 to 50% by weight of a fluororesin.
A low-temperature oxidation catalyst comprising a large surface area carrier and a catalyst component which is added at a ratio of 3 and heated at a temperature of 300 to 400 ° C. 4. A mixture of metal oxides comprising a mixture of manganese dioxide and cupric oxide with silver oxide or nickel oxide.
The low temperature oxidation catalyst according to claim 3, which is compounded in a proportion of 5 to 15% by weight. 5. The low temperature oxidation catalyst according to claim 3, wherein the large surface area carrier is a hydrophobic activated carbon.