JPH0312934B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a gold oxide that can easily burn these combustion gas at a relatively low temperature at relatively low temperature, regarding the combustion catalyst for combustion gas such as hydrogen, carbon monoxide, and hydrogen carbon. Regarding catalysts. Conventionally, the catalytic combustion method converts hydrocarbons such as carbon monoxide, methane, and propane into heat by oxidizing them on a catalyst.
It is used in fields such as the removal of harmful components from various types of exhaust gas, including automobile exhaust gas, and the detection of flammable gases in the air, but in recent years, there has been an increase in the number of safe methods that do not emit nitrogen oxides (NOx). As a clean combustion method, its application to various heating, kitchen, and heating equipment is attracting attention. In order to carry out such catalytic combustion safely and efficiently, a highly active and durable oxidation catalyst is required, and platinum-based metal catalysts or transition metal oxide catalysts are usually used. However, platinum-based metal catalysts have low activity against catalytic combustion of carbon monoxide, while transition metal oxide catalysts have low activity against hydrogen and hydrocarbons. There was a desire to develop a catalyst with high activity. The present invention has been made in response to such conventional needs, and in particular, it is an object of the present invention to provide a catalyst that can catalytically burn carbon monoxide, which causes poisoning symptoms even in minute amounts, at low temperatures. The present invention has been made to achieve such an object, and provides a gold-based oxide composite catalyst comprising gold and an oxide of at least one metal selected from the group consisting of manganese, iron, cobalt, nickel, and copper. It is. Here, oxides of manganese, iron, cobalt, nickel and copper are chemically known as MnO ₂ , Fe ₂ O ₃ ,
Represented by Co ₃ O ₄ , NiO and CuO, an aqueous solution of chloroauric acid (HAuCl ₄ ) and manganese (), iron (),
Cobalt (), Nickel (), and Copper ()
Co-precipitating neutralized salts by reacting an aqueous solution of a neutralizing agent such as an alkali carbonate, an alkali hydroxide, or ammonia with a mixed solution of an aqueous salt solution such as a chloride, sulfate, or nitrate, and then firing. It is obtained by In the case of manganese-gold oxides,
A mixed aqueous solution of the water-soluble salt of manganese () and chloroauric acid is reacted with a mixed aqueous solution of the neutralizing agent and an oxidizing agent such as potassium permanganate, sodium hypochlorite, and sodium bromate to cause coprecipitation. You can also do that. Alternatively, gold and the hydroxide of the metal may be precipitated separately, and then both precipitates may be kneaded. Next, the obtained precipitate is washed with water, dried, and then calcined in the presence of air, usually at 300 to 700°C, to prepare a catalyst. The content of gold in the resulting catalyst is usually 1 to 50 atomic %, preferably 2 to 20 atomic %, most preferably 2 to 10 atomic %. Here, atomic % is the percentage of the number of atoms of a specific metal in the catalyst to the number of atoms of all metals constituting the catalyst. For example, atomic % of Au is (number of Au atoms /
It is expressed as (number of atoms of all metals) x 100. The catalyst of the present invention may be used alone in the form of granules or molded bodies depending on the purpose of use, or
Alternatively, it may be supported on an inorganic heat-resistant substance such as alumina or silica. Furthermore, the catalyst of the present invention is used as a catalyst for complete flameless combustion of hydrogen, carbon monoxide, and hydrocarbon-based combustible gases. Here, the hydrocarbon-based combustible gases include not only lower aliphatic hydrocarbons such as methane, ethane, propane, and butane, but also lower aromatic hydrocarbons such as benzene, toluene, and xylene, cyclohexene,
It contains lower alicyclic hydrocarbons such as cyclohexane and acid-containing organic compounds such as methanol and alcohol. The catalyst of the present invention has higher catalytic activity than a catalyst using only gold, a gold oxide, or a transition metal oxide such as manganese or cobalt. For example, as described below, gold oxide (Au ₂ O ₃ ), cobalt oxide (Co ₃ O ₄ ), manganese oxide (MnO ₂ )
Each of these alone requires a temperature of 80°C or higher to initiate catalytic combustion of hydrogen, as shown in the curves in Figure 1, but by combining these, temperatures of 20°C or higher are required.
Combustion can be started. In addition, the gold-based oxide catalyst of the present invention exhibits extremely high activity for catalytic combustion of carbon monoxide, and in particular, the Fe-Au-based oxide catalyst exhibits extremely high activity even below -30°C, as shown in the rightmost curve in Figure 3. Carbon monoxide can be completely combusted. As described above, the catalyst of the present invention can catalytically burn combustible gases such as hydrogen and carbon monoxide at low temperatures, so it can be used as a combustor that does not cause air pollution or fire hazards, and can be used for various types of heating, kitchens, and food. It is expected to be used in drying and heating processes in industry and the pharmaceutical industry, and its practical advantages are extremely large. Furthermore, since it can be used even below room temperature, it can also be used in filters for removing carbon monoxide from the air and gas masks. Examples of the present invention will be described below. Example 1 77.5g of manganese nitrate hexahydrate and chloroauric acid tetrahydrate
Add 1500ml of a mixed aqueous solution of 20.6g to 1000ml of a mixed aqueous solution of 28.4g of potassium permanganate and 43.9g of sodium carbonate.
ml over about 10 minutes with stirring, and stirring was continued for about 2 hours after the addition was completed. The thus obtained precipitate was thoroughly washed with water by repeating the decanting process several times, and then filtered. This is 120
After drying for 12 hours at °C, crush and store at 400 °C under air circulation.
The mixture was calcined for 5 hours to obtain a Mn-Au based oxide catalyst (atomic % 90:10). This was sieved and used as a catalyst. Example 2 109 g of ferric nitrate nonahydrate and 12.4 g of chloroauric acid tetrahydrate
1500 ml of a mixed aqueous solution of 57.2 g of sodium carbonate was added over about 10 minutes with stirring,
Stirring was continued for about 2 hours after the addition was completed. The thus obtained precipitate was thoroughly washed with water by repeating the decanting process several times, and then filtered. This is 120
After drying for 12 hours at °C, crush and store at 400 °C under air circulation.
The mixture was fired for 5 hours to obtain an Fe-Au based oxide catalyst (atomic % 90:10). This was sieved and used as a catalyst. Example 3 Using an oxide catalyst containing gold and at least one of manganese, iron, cobalt, nickel, and copper obtained in the same manner as in Example 1 or 2,
The catalytic combustion activity towards hydrogen was investigated. Each catalyst was calcined at 400 DEG C. for 5 hours and pulverized into 42-70 mesh, 0.30 g of which was used, and an air mixed gas containing 1% by volume of hydrogen was passed through at 100 ml/min. The results are shown in FIG. 1 and Table 1.

[Table] As is clear from Table 1, the catalytic activity of the oxide is greatly improved by complexing it with gold. This is shown by the comparison with T1/2 (temperature at which 50% of hydrogen is burned out) of comparative examples that do not contain any gold, such as MnO ₂ alone or Fe ₂ O ₃ alone, as shown by the addition of gold. This is evident from the significant decrease in T1/2. Example 4 Fe-Au system obtained by the same method as Example 2,
The relationship between the 50% combustion rate temperature (T1/2) of hydrogen and the gold content when using Co-Au-based and Ni-Au-based composite oxide catalysts was investigated. The results are shown in Figure 2. As is clear from Figure 2, gold is
Just by adding atomic percent, T1/2 decreases rapidly, and a remarkable improvement in activity is observed. Further, as the amount of gold added increases, T1/2 decreases further, and T1/2 decreases at 5 atom% for Fe-Au and Co-Au systems, and at 10 atom% for Ni-Au systems. is the lowest, and if the gold content is higher than that, T1/2 becomes higher. Therefore, in these gold-based composite oxides, there is an optimum gold content at which the maximum activity is obtained, and it is most desirable that the gold content be 5 to 10 atomic percent. In particular, in the Fe-Au system, T1/2 was 39°C at 5 atomic % gold, and the most active catalyst was obtained. Example 5 Fe-Au obtained in Example 4 (atomic % 95:5)
The catalytic combustion activity against carbon monoxide was investigated for Co-Au (atomic % 91:10) oxide and Ni-Au (atomic % 90:10) oxide. The results are shown in Figure 3. The measurement conditions were exactly the same as in Example 4 except that hydrogen was replaced with carbon monoxide. It is clear that the above three types of composite oxide catalysts easily oxidize carbon monoxide at temperatures below 0°C and have extremely high catalytic activity. Hopcalite catalysts, conventionally commercially available as carbon monoxide oxidation catalysts, require temperatures approximately 70° C. higher to achieve the same activity as the catalysts of the present invention. Furthermore, palladium catalysts supported on alumina or silica are generally the best oxidation catalysts, but it was found that their activity was extremely low compared to the catalyst of the present invention. Furthermore, catalysts with gold supported on alumina do not exhibit catalytic activity until the temperature exceeds 300°C, and it is clear that combining gold with oxides of iron, cobalt, and nickel significantly increases the activity. be. As in the case of hydrogen combustion (Example 3), the combustion of carbon monoxide requires high temperatures when using only cobalt or iron oxides, and for this reason, it is necessary to combine gold and these oxides. The effect of improving activity is clear. Example 6 Fe-Au containing 5 at% of gold obtained in Example 4
When X-ray diffraction was measured for the oxides of Co-Au, Co-Au, and Ni-Au, the results shown in Figures 4 and 5 were obtained. This X-ray diffraction pattern revealed that gold existed in a metallic state. Therefore, gold and iron,
The composite effect with transition metal oxides such as cobalt does not appear due to the formation of a new composite oxide phase, but is thought to be due to the effect of fine particulate gold dispersed in these transition metal oxides. A similar effect can be expected by adding fine gold particles by vapor deposition or by kneading previously prepared gold colloid fine particles and the transition metal oxide. Therefore, the above 2
When a Fe ₂ O ₃ -Au-based composite was prepared in the same manner and the catalytic activity was measured, almost the same activity as the catalyst obtained in Example 4 was obtained. Example 7 Cobalt nitrate hexahydrate 29g, manganese nitrate hexahydrate
1000ml mixed aqueous solution of 3.5g and 2g of metal chloride tetrahydrate
was added to 500 ml of a mixed aqueous solution of 1.3 g of potassium permanganate and 15.2 g of sodium carbonate while stirring.
The mixture was added within a few minutes, and stirring was continued for about 2 hours after the addition was completed. The thus obtained precipitate was thoroughly washed with water by repeating the decanting process several times, and then filtered. This at 120℃
The Co-Mn-Au based oxide catalyst (atomic%
80:16:4). This was sieved and used as a catalyst. When the activity against hydrogen combustion was investigated under the same conditions as in Example 3, a high combustion rate was obtained at low temperatures as shown in the curve of FIG. hydrogen 50
The % combustion rate temperature is 69°C, which is 50°C or more lower than when Co ₃ O ₄ , MnO ₂ , Au ₂ O ₃ or Au that constitute this ternary composite oxide is used alone, and the present invention It has become clear that this effect also appears in ternary composite oxides. Example 8 Various types of Co-Mn-Au were prepared in the same manner as in Example 7.
A system composite oxide is prepared, the atomic ratio of cobalt to manganese is Co/Mn=20/4, and cobalt 20
The number of gold atoms (X) relative to atoms was varied. Co-Mn-Au (atomic ratio 20:4:
X) As a result of measuring the catalytic activity of the composite oxide for hydrogen combustion, the relationship between X and the temperature required for 50% hydrogen combustion (T1/2, °C) was as shown in Figure 6. As is clear from the figure, Co− does not contain gold.
Mn (atomic ratio 20:4) composite oxide alone has T1/2.
In contrast, T1/2 was as high as 130°C, whereas in those containing gold with X=1 or more, T1/2 was about 70°C, and the catalyst activity was significantly improved by adding gold.

[Brief explanation of drawings]

Figure 1 shows catalytic combustion of a dilute hydrogen/air mixture.
The catalyst used was: Fe/Au=19/1:
Co/Mn/Au=20/4/1, :Au, :
_{Au2O3 ,} : _{Co3O4 ,} :NiO, : _MnO2 ,
:Fe ₂ O ₃ , Figure 2 shows the dependence of hydrogen catalytic combustion start-up temperature (T1/2) on gold content. Figure 3 shows the temperature dependence of the catalytic combustion rate of carbon monoxide. Figure 4 shows
X-ray diffraction patterns of nickel-gold and cobalt-gold catalysts, Ni-Au system: Ni/Au = 19/1, surface area 54 m ² /g, Co-Au system: Co/Au = 19/1, surface area 79m ² /g, Figure 5 is the X-ray diffraction pattern of the iron-gold catalyst. Figure 6 shows the gold content dependence of the catalytic combustion start-up temperature of a Co-Mn-Au composite oxide catalyst.

Claims (1)

[Claims] 1. A catalyst for catalytic combustion of combustible gas, comprising gold and at least one metal oxide selected from the group consisting of manganese, iron, cobalt, nickel, and copper.