JPS6313728B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a combustion catalyst for generating high-temperature gas in a device that utilizes high-temperature gas obtained by catalytic combustion of fuel, and in particular to a combustion catalyst that supports a noble metal on a specific carrier and exhibits little performance deterioration even at high temperatures. Regarding. [Prior art] The catalytic combustion method, which promotes the reaction between fuel and oxygen on a catalyst, has the following advantages compared to the normal burner combustion method (flame combustion): (1) Complete combustion is possible at a lower temperature; (2) It has the following characteristics: stable combustion is possible over a wide range of fuel/air ratios, and (3) almost no thermal NOx is generated.
It has received particular attention in recent years. Conventionally, the applications of catalytic combustion technology include (1) oxidation treatment of organic solvents and bad odors; (2)
Examples include automobile exhaust gas treatment, (3) catalytic combustion heaters, etc. Recently, development efforts have been underway in various places to apply catalytic combustion technology that takes advantage of the above characteristics to large-capacity boilers, gas turbines, aircraft jet engines, and the like. This is a technology that uses high-temperature gas (or high-pressure gas) obtained by catalytic combustion of fuel, and is essentially different from processes for removing harmful components such as automobile exhaust gas treatment and odor removal. be. The operating temperature of the catalyst is usually 400°C or higher, and in some cases reaches 1400°C to 1500°C.
For this reason, it is required that the catalyst has catalytic activity over a temperature range of 400°C to 1400°C or higher, and that thermal deterioration of the catalyst is particularly small at high temperatures. Conventionally, the temperature used in the catalytic combustion method is 200 to 500°C for purposes such as removing bad odors, and even in the case of automobile exhaust gas treatment, which uses the highest temperature, the maximum temperature is 800 to 900°C. In general, catalysts are made of precious metals, especially platinum, on carriers such as alumina and silica, which have a large specific surface area.
Those carrying palladium, rhodium, etc. are used. Such noble metal catalysts are thermally stable compared to other metal oxide catalysts, so they are used even under temperature conditions of 800 to 900°C, such as in automobile exhaust gas treatment. However, when catalysts are used in a process that extracts thermal energy from chemical energy by catalytic combustion of fuel, the reaction temperature is 1000℃ or higher, and depending on the conditions, 1400℃ or 1500℃.
It reaches up to ℃. Under such conditions, even noble metal catalysts undergo thermal deterioration, resulting in a noticeable drop in performance.
This may be due to agglomeration of noble metals dispersed in fine particles on the carrier at high temperatures or a decrease in the specific surface area of the carrier due to sintering of the carrier. [Objective of the Invention] The object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, to support a noble metal on a carrier that suppresses agglomeration of noble metal components under high temperature conditions, and with less decrease in specific surface area due to sintering, An object of the present invention is to provide a combustion catalyst that exhibits little performance deterioration even at high temperatures. [Summary of the Invention] To summarize the present invention, the combustion catalyst of the present invention is a noble metal-supported combustion catalyst for generating high temperature gas in an apparatus that utilizes high temperature gas obtained by catalytic combustion of fuel, and the support is made of titania. It is characterized by comprising a first component and a second component which is an oxide of one or more metals selected from the group consisting of magnesium, strontium, lanthanum, yttrium, cerium, zirconium, silicon, and tin. The present inventors have repeatedly investigated various types of carriers that have the effect of suppressing agglomeration of precious metal fine particles at high temperatures. By using titania as a carrier, the precious metal component can be reduced compared to when using a conventional alumina carrier. It was found that aggregation becomes less likely to occur.
The reason for this is presumed to be that the noble metal component and titania exhibit a strong interaction. However, it has been found that when only titania is used as a carrier, titania sinters rapidly at temperatures above 700°C, resulting in a large decrease in specific surface area and a decrease in activity. Therefore, the present inventors developed a second species of Titania.
As a result of investigating a method of suppressing sintering by adding components, we added magnesium, strontium, lanthanum, and
The present invention was achieved by discovering that it is sufficient to add an oxide of one or more metals selected from the group consisting of ytrium, cerium, zirconium, silicon, and tin. According to the present invention, a combustion catalyst with excellent activity and durability can be obtained by supporting a noble metal component on a carrier that is a combination of such a metal oxide and titania. In addition, the titania-based carrier according to the present invention has the advantage that it has SOx resistance and is less likely to deteriorate even if sulfur compounds are contained in the fuel, compared to ordinary alumina carriers. (Alumina carriers often degenerate into aluminum sulfate.) The titania-based carrier in the present invention has a composition ratio of titania as a first component and metal oxide as a second component to titanium in an atomic ratio of 1 to 1. It is particularly preferable that the second component metal is in a range of 0.05 to less than 1.0. If the ratio of the second component metal is less than the above 0.05, the effect of its addition will be insufficient and sintering of titania will be large; if it is more than 1.0, the ratio of titania will be too small and the effect as a titania-based carrier will be reduced. This is undesirable as it reduces the number of Titanium raw materials for preparing the carrier in the present invention include various titania, titanic acid (TiO ₂ .nH ₂ O) that produces titania by heating, titanium tetrachloride, titanium sulfate, titanyl sulfate, etc. can be used. Alternatively, a desirable method is to neutralize an aqueous solution of titanium tetrachloride, titanium sulfate, etc. with aqueous ammonia, caustic alkali, alkali carbonate, urea, etc. to form a precipitate, and then thermally decompose this to obtain an oxide. be. or,
Organotitanium compounds such as titanium tetraisopropoxide can also be used. As the raw material for the second component, any of the aforementioned various metal oxides, hydroxides, chlorides, nitrates, sulfates, acetates, oxalates, etc. can be used. In the production of the carrier in the present invention, any of the precipitation methods, coprecipitation methods, kneading methods, impregnation methods, etc. used in normal production can be used. The titanium raw material and the second component raw material may be mixed in advance to form the final oxide, or the respective oxides may be prepared in advance and then thoroughly mixed and kneaded. The carrier may be formed by any method such as a tableting method, an extrusion method, or a rolling granulation method. Alternatively, a honeycomb-shaped refractory carrier or the like may be impregnated with the carrier component in the method of the present invention and fired to form an oxide layer on the surface, or titania and the second component metal may be coated on the surface by a method such as coating. A carrier on which an oxide layer is formed can also be used. Effective noble metal components used in the combustion catalyst of the present invention include platinum, palladium, ruthenium, iridium, and rhodium. These components can also be used in the form of alloys or mixtures. As a method for supporting the noble metal component, any method such as an impregnation method or a kneading method may be used, but in order to effectively utilize the noble metal component, it is preferable to support the noble metal component on the surface of the carrier by an impregnation method. Examples of the raw materials that can be used include salts and complex salts such as chloroplatinic acid, ammonium bromoplatinate, palladium chloride, palladium nitrate, rhodium chloride, ruthenium chloride, and iridium chloride. In addition to noble metal components, active ingredients include:
A transition metal component such as nickel, cobalt, manganese, chromium, etc. may be included as a promoter component. Various gaseous fuels and liquid fuels can be used as the fuel when performing catalytic combustion using the catalyst according to the present invention. Suitable fuels include, for example, aliphatic hydrocarbons such as methane, ethane, propane and butane, petroleum distillates such as gasoline, naphtha, kerosene and gas oil, alcohols such as methanol and ethanol, and hydrogen and carbon monoxide. can be mentioned. When using solid fuel such as coal, it can be used as a fuel after being gasified or liquefied in advance. Of course, dilute fuels containing inert substances, such as low-calorie coal gas and coke oven gas, can also be used. The fuel can be efficiently combusted over a wide reaction temperature range of 400°C to 1500°C, preferably 450°C to 1400°C. At temperatures exceeding 1500°C, even the catalyst according to the present invention is undesirable because the activity decreases significantly due to sintering and evaporation of the noble metal component. It is possible to use the combustion catalyst of the invention even at temperatures below 400°C. In particular, in the case of highly combustible fuels such as hydrogen, they can burn efficiently even at temperatures below 400°C. In addition, in combustion reactions, the temperature rise due to the reaction is large, so the temperature at which the reaction starts,
In other words, even if the ignition temperature is lower than 400°C, the combustion temperature range may exceed 1000°C. In such cases, there is of course a temperature range below 400°C in which the catalyst of the present invention can be used. Hereinafter, the case where the catalyst of the present invention is utilized in a gas turbine will be specifically explained with reference to the accompanying drawings. That is, the accompanying drawing is a schematic diagram of an example of an apparatus using the catalyst of the present invention. In the drawings, reference numeral 1 indicates a compressor, 2 indicates a catalytic combustor, 3 indicates a gas turbine, 4 indicates a generator, and 5 indicates a steam turbine. As shown in the diagram, a portion of the air sent to the gas turbine is sent to the catalytic combustor via the compressor.
Preferably, it is used as a fuel oxidizer. [Examples of the present invention] Next, the present invention will be explained using Examples and Comparative Examples, but the present invention is not limited by these in any way. Example 1 and Comparative Examples 1 and 2 (1) Preparation of catalysts Platinum-titania-magnesia-based catalyst (Example 1), and for comparison, platinum-titania-based catalyst (Comparative Example 1) and platinum-alumina-based catalyst Each of the catalysts (Comparative Example 2) was prepared as follows. (a) Catalyst of Example 1 Take 500 g of metatitanic acid slurry (TiO ₂
150g) and 240g of magnesium nitrate.
g was added. Further, 500 ml of distilled water was added, and the mixture was thoroughly kneaded using a kneader. After preliminarily baking the resulting paste-like mixture at 300° C. for 5 hours, 3% by weight of graphite was added and the mixture was compressed into tablets with a diameter of 3 mm and a thickness of 3 mm at a molding pressure of about 500 Kg/cm ² . The obtained molded product was fired at 700°C for 4 hours. Next, it was impregnated with 100 ml of hexachloroplatinic acid aqueous solution, dried at 120°C for 5 hours, and then calcined in air at 1000°C for 3 hours. The composition of the carrier was 1 part titanium to 0.5 part magnesium, and the amount of platinum supported was 1% by weight based on the part of the carrier. (b) Catalyst of Comparative Example 1 After preliminarily calcining 500 g of metatitanic acid slurry at 300°C for 5 hours, 3% by weight of graphite was added, and a molding pressure of about 500 Kg/cm ² was applied to form a catalyst with a diameter of 3 mm.
It was molded into tablets with a thickness of 3 mm. The obtained molded product was fired at 700°C for 4 hours. Next, it was impregnated with 50 ml of hexachloroplatinic acid aqueous solution (3 g Pt/100 g aqueous solution) and dried at 120°C for 5 hours.
It was fired in air at 1000°C for 3 hours. In the obtained catalyst, the amount of platinum supported was 1% by weight based on the titania carrier. (c) Catalyst of Comparative Example 2 Hexachloroplatinic acid aqueous solution (2.5gPt/100
g aqueous solution) 40ml to 3ml spherical alumina carrier
It was impregnated with 100 g, dried at 120°C for 5 hours, and then fired in air at 1000°C for 3 hours. The amount of platinum supported in the obtained catalyst was 1% by weight of the alumina support.
It was hot. (2) Performance test of catalyst Performance tests of the three types of catalysts prepared in (a), (b), and (c) above were conducted as follows. Each quartz glass reaction tube with an inner diameter of 20 mm was filled with 8 ml of catalyst and heated from the outside in an electric furnace to preheat the gas entering the catalyst layer to 500°C. A gas with a composition of 3% methane and the balance air was flowed into the reaction tube at a space velocity of 50,000 h ^-1 ,
A continuous time test was conducted. Methane at the inlet and outlet of the catalyst layer was measured using an FID type gas chromatograph to determine the reaction rate. By burning methane,
The temperature of the catalyst layer reached around 1200°C. The results obtained are shown in Table 1 below.

[Table] As is clear from Table 1, the catalyst of Example 1 according to the present invention is superior to the catalysts of Comparative Examples 1 and 2 in both activity and durability. Example 2 and Comparative Examples 3 and 4 (1) Preparation of catalysts Palladium-titania-zirconia-based catalyst (Example 2), and for comparison, palladium-titania-based catalyst (Comparative Example 3) and palladium-alumina-based catalyst The catalysts (Comparative Example 4) were prepared as follows. (a) Catalyst of Example 2 500 g of titanium tetrachloride (TiCl ₄ ) solution was dissolved in 1 part of distilled water. This solution was gradually dropped into a 1N aqueous sodium hydroxide solution to form a precipitate of titanic acid. The resulting precipitate was filtered by decantation, thoroughly washed with distilled water, and then zirconyl nitrate [ZrO
(NO ₃ ) _{2.2H 2} O] (352 g) was added and thoroughly kneaded with a kneader. The resulting paste-like mixture was preliminarily calcined at 300°C for 5 hours, and then molded and calcined in the same manner as the catalyst preparation method of Example 1. Next, it was impregnated with 100ml of palladium nitrate aqueous solution, dried at 120℃ for 5 hours, and then
It was baked at 1000°C for 3 hours. The composition of the carrier was 1 part titanium to 0.5 part zirconium in atomic ratio. The amount of palladium supported is 2
It was in weight%. (b) Catalyst of Comparative Example 3 A titanic acid precipitate was prepared in the same manner as in the preparation of the catalyst of Example 2, and after washing and filtering,
Preliminary firing was performed at 300°C for 5 hours. Mold this,
After baking at 700℃, palladium nitrate aqueous solution
60ml was impregnated, dried at 120°C for 5 hours, and then calcined in air at 1000°C for 3 hours. The resulting catalyst contained 2% palladium by weight based on the support. (c) Catalyst of Comparative Example 4 100 g of a commercially available alumina carrier was impregnated with 60 ml of an aqueous palladium nitrate solution, dried at 120°C for 5 hours, and then calcined in air at 1000°C for 3 hours. The resulting catalyst contained 2% palladium by weight based on the support. (2) Performance test of catalyst Performance tests of the three types of catalysts prepared in (a), (b), and (c) above were conducted in the same manner as in Example 1.
The results obtained are shown in Table 2 below.

[Table] As is clear from the results in Table 2, the catalyst of Example 2 according to the present invention was superior in activity and durability compared to the catalysts of Comparative Examples 3 and 4, and the catalyst of Example 2 according to the present invention was superior in activity and durability. The effect is obvious. Example 3 Five types of catalysts were prepared using the same components as the catalyst carrier of Example 1 (titania and magnesia) but with different compositions, and their performance tests were conducted in the same manner as in Example 1. The results obtained are shown in Table 3 below.

[Table] As is clear from Table 3, when the composition ratio of titania and magnesia is in the range of 0.05 to less than 1.0 atomic ratio of magnesium to 1 titanium (numbers 2 to 4), a catalyst with particularly excellent performance can be obtained. can get. Note that almost similar results were obtained when a second component other than magnesium was used. Example 4 In the catalyst of Example 1, strontium oxide, lanthanum oxide, ittria, ceria, zirconia, silica, or tin oxide was used instead of magnesia as the second component, and a carrier in which these were combined with titania was used. Eight types of catalysts were prepared and their performance tests were conducted in the same manner as in Example 1. The results obtained are shown in Table 4 below.

【table】

[Table] As is clear from Table 4, the catalysts according to the present invention are all excellent in both activity and durability. Example 5 In this example, titania, zirconia,
3 combinations of silica, titania/zirconia/ceria, and titania/magnesia/lanthanum oxide
A seed carrier was prepared, and a catalyst was prepared in which 0.5% by weight of palladium as a noble metal was supported on the carrier, and its performance was examined in the same manner as in Example 1. The compositions of the carriers and the performance test results of catalysts using them are shown in Table 5 below.

〔Effect of the invention〕

As described above, according to the present invention, a combustion catalyst having excellent performance can be provided by supporting a noble metal on a carrier made of a combination of titania and a specific metal oxide.

[Brief explanation of the drawing]

The drawing is a schematic diagram of an example of an apparatus using the catalyst of the present invention. 1: compressor, 2: catalytic combustor, 3: gas turbine, 4: generator, 5: steam turbine.

Claims (1)

[Scope of Claims] 1. A noble metal-supported combustion catalyst for producing high-temperature gas in an apparatus that utilizes high-temperature gas obtained by catalytic combustion of fuel, in which the carrier comprises a first component of titania, magnesium, strontium, lanthanum, and yttrium. , and a second component consisting of an oxide of one or more metals selected from the group consisting of cerium, zirconium, silicon, and tin. 2 Claims in which the composition ratio of the first component titania and the second component metal oxide in the carrier is in the range of 0.05 to less than 1.0 of the second component metal to titanium 1 to titanium atomic ratio. The combustion catalyst according to item 1.