JP2011218320A - Fuel reforming catalyst - Google Patents

Abstract

Provided is a fuel reforming catalyst capable of improving the durability of a catalyst when reforming the fuel by using exhaust gas from an internal combustion engine or a solid oxide fuel cell as a heat source.
A fuel reforming catalyst is obtained by loading a noble metal catalyst on a carrier made of γ-alumina and carrying 5 to 30% by mass of cerium oxide on the carrier. The noble metal is preferably ruthenium, and 10 to 20% by mass of the cerium oxide is preferably substituted with zirconium oxide.
[Selection] Figure 2

Description

  The present invention relates to a fuel reforming catalyst.

  For example, it is known to use a gas containing hydrogen, carbon monoxide, carbon dioxide, methane, or the like as a fuel for a solid oxide fuel cell. The gas is produced by reacting hydrocarbon or alcohol with steam or air and reforming. Typical reforming methods include steam reforming, carbon dioxide reforming, autothermal reforming, partial oxidation. Modification etc. can be mentioned.

  Here, examples of the hydrocarbon include gaseous fuels such as city gas and biogas, and petroleum-based liquid hydrocarbon fuels such as gasoline, kerosene, and diesel oil. Examples of the alcohol include methanol, ethanol, butanol and the like.

  Conventionally, as a fuel reforming catalyst for reforming fuel by the reforming reaction, for example, a catalyst in which a Ru catalyst is supported using α-alumina as a carrier is known. The fuel reforming catalyst is used for reforming hydrocarbons, particularly kerosene, and the reaction temperature is particularly preferably 650 to 800 ° C. (see Patent Document 1).

  Further, as a fuel reforming catalyst for reforming fuel by the reforming reaction, a catalyst in which a catalyst made of any of Al, Cu, Zn, Pt, and Pd is supported using γ-alumina as a carrier is known. (See Patent Documents 2 to 4).

Japanese Patent No. 4358405 JP-A-8-215576 JP 2001-300315 A JP 2006-82996 A

  However, in the conventional fuel reforming catalyst, when the fuel is reformed using the exhaust gas from an internal combustion engine or a solid oxide fuel cell as a heat source, the catalyst deteriorates due to carbon deposition and the fuel conversion rate decreases. There is a disadvantage that it is difficult to reform the fuel having 2 or more carbon atoms.

  The present invention eliminates such inconvenience, and improves the durability of the catalyst when reforming the fuel using the exhaust gas of an internal combustion engine or a solid oxide fuel cell as a heat source, and also provides a fuel having 2 or more carbon atoms. An object of the present invention is to provide a fuel reforming catalyst that can easily reform the fuel.

  In order to achieve this object, the fuel reforming catalyst of the present invention is a fuel reforming catalyst obtained by loading a noble metal catalyst on a carrier made of γ-alumina, and 5 to 30% by mass of cerium oxide of the carrier. Is supported on the carrier.

  In the fuel reforming catalyst of the present invention, the low temperature activity of the noble metal catalyst is improved by supporting 5 to 30% by mass of cerium oxide of the carrier made of γ-alumina on the carrier. Therefore, according to the fuel reforming catalyst of the present invention, it is possible to obtain an excellent fuel conversion rate even when reforming the fuel by using exhaust gas from an internal combustion engine or a solid oxide fuel cell as a heat source, The durability of the catalyst can be improved by suppressing the deposition of carbon.

  Further, the cerium oxide has an oxygen storage capacity, and when a local oxidizing atmosphere is generated on the fuel reforming catalyst, oxygen is stored, and a local reducing atmosphere is generated on the fuel reforming catalyst. When it occurs, the stored oxygen can be released. As a result, the fuel reforming catalyst of the present invention can easily reform a fuel having 2 or more carbon atoms.

  In the fuel reforming catalyst of the present invention, when the amount of the cerium oxide supported on the carrier is less than 5% by mass, the above effect cannot be obtained. On the other hand, even if the amount of the cerium oxide supported on the carrier exceeds 30% by mass, no further effect can be obtained.

In the fuel reforming catalyst of the present invention, the noble metal is preferably ruthenium. In the fuel reforming catalyst of the present invention, the γ-alumina has a specific surface area in the range of 100 to 300 m ² / g, a pore volume in the range of 0.2 to 0.7 cm ³ / g, And a packing density in the range of ^{4 to} 0.9 g / cm ³ .

  In the fuel reforming catalyst of the present invention, it is preferable that 10 to 20% by mass of the cerium oxide is substituted with zirconium oxide. In the fuel reforming catalyst of the present invention, when the cerium oxide in the above range is substituted with the zirconium oxide, when reforming the fuel using exhaust gas from an internal combustion engine or a solid oxide fuel cell as a heat source, Further, the low temperature activity of the noble metal catalyst can be improved and carbon deposition can be suppressed.

  When the amount of substitution by zirconium oxide is less than 10% by mass of the cerium oxide, the effect of further improving the low temperature activity of the noble metal catalyst and suppressing carbon deposition cannot be obtained. Further, even if the amount of substitution by zirconium oxide exceeds 20% by mass of the cerium oxide, no further effect can be obtained.

  Moreover, in the fuel reforming catalyst of the present invention, the heat resistance of the fuel reforming catalyst is improved and aggregation of the fuel reforming catalyst is prevented by replacing the cerium oxide in the range with the zirconium oxide. And excellent durability can be obtained.

The system block diagram which shows the example of 1 structure of the fuel reformer using the fuel reforming catalyst of this invention. The graph which shows the relationship between the reforming temperature and the fuel conversion rate in the fuel reforming using the fuel reforming catalyst of the present invention.

  Next, embodiments of the present invention will be described in more detail.

  The fuel reforming catalyst of the present embodiment is a fuel reforming catalyst in which a noble metal catalyst is supported on a carrier made of γ-alumina, and 5 to 30% by mass of cerium oxide of the carrier is supported on the carrier. Become.

  The fuel reforming catalyst of this embodiment modifies the fuel into a gas containing hydrogen, carbon monoxide, carbon dioxide, methane, etc. by steam reforming, autothermal reforming, carbon dioxide reforming, partial oxidation reforming, or the like. Used for quality.

  Examples of the fuel that is the target of the fuel reforming catalyst of the present embodiment include gaseous hydrocarbon fuel, liquid petroleum hydrocarbon fuel, alcohol fuel, mixed fuel thereof, gaseous or liquid synthetic fuel, and the like. be able to. As the hydrocarbon fuel, one having an average carbon number of about 1 to 17 can be used. As the alcohol fuel, methanol, ethanol, butanol, or the like can be used. The alcohol fuel may contain about 1 to 90% by mass of water based on the total amount.

  In the fuel reforming catalyst of the present embodiment, the noble metal catalyst acts as a main catalyst for fuel reforming. As the noble metal catalyst, one kind of metal selected from the group consisting of Ru, Rh, Pt, Ir, Co, Fe, Ni, Mn, and Mg can be used, but the balance between catalytic activity and price is good. Therefore, Ru is preferable.

  The noble metal catalyst can be supported on the carrier in the range of 0.1 to 15% by mass of the carrier, for example, but is preferably supported in the range of 1 to 8% by mass. The noble metal catalyst preferably has an average particle size in the range of 1 to 30 nm, and more preferably has an average particle size in the range of 1 to 10 nm, in order to be used for the fuel reforming. preferable.

Since the γ-alumina is used as the carrier for the noble metal catalyst in the fuel reforming, the specific surface area in the range of 100 to 300 m ² / g and the fine surface area in the range of 0.2 to 0.7 cm ³ / g are used. It is preferable to have a pore volume and a packing density in the range of 0.4 to 0.9 g / cm ³ .

  In the fuel reforming catalyst of the present embodiment, the cerium oxide acts as a promoter and can improve the low temperature activity of the noble metal catalyst. Therefore, according to the fuel reforming catalyst of the present embodiment, an excellent fuel conversion rate can be obtained even when reforming the fuel using the exhaust gas of the internal combustion engine or the solid oxide fuel cell as a heat source. Further, the durability of the catalyst can be improved by suppressing the deposition of carbon.

  Further, the cerium oxide has an oxygen storage capacity, and when a local oxidizing atmosphere is generated on the fuel reforming catalyst, oxygen is stored, and a local reducing atmosphere is generated on the fuel reforming catalyst. When it occurs, the stored oxygen can be released. As a result, the fuel reforming catalyst of the present embodiment can easily reform the fuel having 2 or more carbon atoms.

  In the fuel reforming catalyst of the present embodiment, the above-described effects cannot be obtained when the amount of the cerium oxide supported on the carrier is less than 5% by mass. On the other hand, even if the amount of the cerium oxide supported on the carrier exceeds 30% by mass, no further effect can be obtained.

  In the fuel reforming catalyst of this embodiment, 10 to 20% by mass of the cerium oxide is preferably substituted with zirconium oxide or lanthanum oxide, and more preferably substituted with zirconium oxide. As a result, the fuel reforming catalyst of the present embodiment further improves the low-temperature activity of the noble metal catalyst when reforming the fuel using the exhaust of an internal combustion engine or a solid oxide fuel cell as a heat source, Precipitation can be suppressed.

  When the amount of substitution with zirconium oxide or lanthanum oxide is less than 10% by mass of the cerium oxide, the effect of suppressing the carbon deposition by further improving the low temperature activity of the noble metal catalyst cannot be obtained. Further, even if the amount of substitution with zirconium oxide or lanthanum oxide exceeds 20% by mass of the cerium oxide, no further effect can be obtained.

  In the fuel reforming catalyst of the present embodiment, the heat resistance of the fuel reforming catalyst is improved by replacing the cerium oxide in the range with the zirconium oxide or lanthanum oxide, and the fuel reforming catalyst. Aggregation can be prevented, and excellent durability can be obtained.

  The fuel reforming catalyst of the present embodiment can be manufactured as follows.

  First, a coating layer of cerium oxide serving as a co-catalyst is formed on γ-alumina serving as a carrier, and the carrier is fired at a temperature in the range of 400 to 750 ° C. for 1 hour or more in air or an oxygen-containing gas. The cocatalyst is supported on the catalyst. The cerium oxide coating layer can be formed by a method known per se such as an impregnation method, a wet adsorption method, a roll mill adsorption method, a spray method, a sputtering method, a CVD method, a coating method, a mechanochemical method, and a sol-gel method. Any of the above methods may be used.

  Next, a coating layer of the noble metal as a main catalyst, for example, Ru, is formed on the carrier on which the promoter is supported, and is heated to 30 ° C. in the atmosphere, an oxygen-containing gas, or an inert gas at a temperature in the range of 100 to 600 ° C. The main catalyst is supported on the carrier by performing calcination for at least minutes, preferably for 1 hour or more. The formation of the noble metal coating layer may be carried out by any of the methods known per se, as in the formation of the cocatalyst coating layer. The main catalyst is preferably calcined at a lower temperature than the cocatalyst.

  And the support | carrier with which the said main catalyst and the co-catalyst were carry | supported is finally heated in the range of 300-700 degreeC in reducing atmosphere, and the fuel reforming catalyst of this embodiment can be obtained. In addition, it is preferable that the fuel reforming catalyst of this embodiment does not bear a heat history of 700 ° C. or higher in the manufacturing method. When a thermal history of 700 ° C. or higher is given, the γ-alumina undergoes a phase change, the surface area is significantly reduced, and the desired performance may not be obtained in the manufactured fuel reforming catalyst.

  The fuel reforming catalyst of the present embodiment produced as described above can be used in a known manner such as a spherical body, a granular body, a honeycomb-shaped body, a foamed body, and a fibrous body.

  Next, examples and comparative examples are shown.

In this example, first, cerium nitrate hexahydrate (Ce (NO ₃ ) ₄ .6H ₂ O) is added to γ-alumina particles having an average particle diameter of 2 mm in terms of the amount of cerium oxide (CeO ₂ ). It was made to adsorb | suck so that it might become 10 mass% of (gamma) -alumina particle | grains, and it dried. Next, the γ-alumina particles adsorbed with cerium nitrate hexahydrate were calcined in air at a temperature of 600 ° C. for 3 hours, and the γ-alumina particles were supported with cerium oxide.

Next, ruthenium nitrate (Ru (NO ₃ ) ₃ ) is added to the γ-alumina particles supporting cerium oxide so that the supported amount is 5% by mass of the γ-alumina particles in terms of ruthenium (Ru). Adsorbed. Next, after ruthenium nitrate is decomposed using potassium hydroxide and pure water, it is dried at a temperature of 100 ° C., and calcined in the atmosphere at a temperature of 350 ° C. for 1 hour, whereby ruthenium is added to the γ-alumina particles. Supported.

  Next, the γ-alumina particles carrying ruthenium and cerium oxide were reduced and calcined at 650 ° C. for 30 minutes in a hydrogen atmosphere to obtain a fuel reforming catalyst.

  Next, the performance of the fuel reforming catalyst obtained in this example was evaluated using the fuel reforming apparatus 1 shown in FIG.

  A fuel reformer 1 shown in FIG. 1 is supplied from a water / fuel mixing unit 4 that mixes fuel supplied from a fuel supply unit 2 and water vapor generated in a steam generation unit 3, and from a water / fuel mixing unit 4. And a fuel reforming section 5 for reforming the mixed fuel of the fuel and water vapor. The fuel reformer 1 also includes a wet flow meter 6 that measures the flow rate of the reformed fuel obtained in the fuel reforming unit 5 and a Fourier transform infrared spectroscopic analyzer that analyzes the composition of the reformed fuel ( FT-IR) 7 and a gas chromatograph (GC) 8.

  The fuel supply unit 2 includes a liquid fuel tank 21 and a gaseous fuel supply system 22. The liquid fuel tank 21 is connected to the water / fuel mixing unit 4 via a liquid fuel conduit 21 a and a fuel conduit 23. On the other hand, the gaseous fuel supply system 22 is connected to the water / fuel mixing section 4 via the gaseous fuel conduit 22a and the fuel conduit 23, and the gaseous fuel conduit 22a joins with the liquid fuel conduit 21a to become the fuel conduit 23. ing.

  Examples of the liquid fuel supplied from the liquid fuel tank 21 include ethanol, gasoline, kerosene, and light oil. In the fuel reformer 1, the liquid fuel tank 21 is replaced according to the supplied liquid fuel. ing. Moreover, city gas, biogas, etc. can be mentioned as gaseous fuel supplied by the gaseous fuel supply system 22, and the fuel reformer 1 switches the gaseous fuel supply system 22 according to the gaseous fuel supplied. ing.

  The water vapor generating unit 3 includes a water tank 31, a heat exchanger 32, and an exhaust gas conduit 33 that supplies exhaust gas to the heat exchanger 32. The water tank 31 is connected to the water / fuel mixing unit 4 through a water conduit 31a, and includes a heat exchanger 32 on the way. The water flowing through the water conduit 31a is heat-exchanged with the exhaust gas supplied through the exhaust gas conduit 33 in the heat exchanger 32 to be converted into water vapor and supplied to the water / fuel mixing unit 4.

  The water / fuel mixing unit 4 includes a mixed fuel conduit 41 and is connected to the fuel reforming unit 5 via the mixed fuel conduit 41. The water / fuel mixing unit 4 mixes the fuel supplied by the fuel conduit 23 and the water vapor supplied by the water conduit 31a, and generates a mixed fuel of, for example, S / C (steam carbon ratio) = 3. The generated mixed fuel is supplied to the fuel reforming unit 5 through the mixed fuel conduit 41.

  The fuel reforming unit 5 includes a fuel reformer 51 that houses a fuel reforming catalyst, and an electric furnace 52 that houses the fuel reformer 51 and heats the fuel reformer 51. The fuel reformer 51 is, for example, a stainless steel pipe having an inner diameter of 16 mm and a length of 160 mm. The mixed fuel conduit 41 is connected to one end and the reformed fuel conduit 53 for taking out reformed fuel is connected to the other end. Has been. The fuel reformer 51 includes a temperature sensor 51a on the outlet side. The fuel reforming unit 51 reforms the mixed fuel supplied by the mixed fuel conduit 41, and the generated reformed fuel is taken out from the reformed fuel conduit 53.

  The reformed fuel conduit 53 is provided with a moisture condenser 54 in the middle, and a wet flow meter 6 is provided downstream of the moisture condenser 54, and the downstream end is connected to the Fourier transform infrared spectrometer 7. . On the other hand, the reformed fuel conduit 53 is provided with a gas chromatograph conduit 55 that branches from between the moisture condenser 54 and the wet flow meter 6, and the downstream end of the gas chromatograph conduit 55 is connected to the gas chromatograph device 8. It is connected.

Next, ethanol was reformed using the fuel reformer 1 shown in FIG. In this embodiment, ethanol is supplied from the fuel supply unit 2 at a space velocity (LHSV) = 1.5 h ⁻¹ and mixed with water vapor so that S / C = 3 in the water / fuel mixing unit 4. The obtained mixed fuel was supplied to the fuel reforming section 5. In the fuel reforming unit 5, the fuel reformer 51 is filled with 15 ml of the fuel reforming catalyst obtained in the present embodiment, and the fuel reformer 51 is heated by the electric furnace 52, so that the fuel reformer 51 The temperature detected by the temperature sensor 51a provided on the outlet side of the gas was in the range of 200 to 700 ° C. Then, the flow rate of the reformed fuel obtained at each temperature is measured by the wet flow meter 6, and the composition of the reformed fuel is analyzed by the Fourier transform infrared spectroscopic analyzer 7 and the gas chromatograph device 8. And the fuel conversion rate was calculated from the composition. FIG. 2 shows the relationship between the reforming temperature and the fuel conversion rate.
[Comparative Example 1]
In this comparative example, the fuel conversion was calculated in exactly the same manner as in Example 1 except that a commercially available ruthenium catalyst was used. FIG. 2 shows the relationship between the reforming temperature and the fuel conversion rate.

  The commercially available ruthenium catalyst uses α-alumina as a carrier and supports 5% by mass of ruthenium of the α-alumina particles, but does not support cerium oxide at all.

  As shown in FIG. 2, according to the fuel reforming catalyst of Example 1, the fuel conversion rate is higher even in the low temperature region than the commercially available ruthenium catalyst of the comparative example. Therefore, according to the fuel reforming catalyst of the present invention, it is apparent that the low-temperature activity of the ruthenium catalyst is improved by supporting 10% by mass of cerium oxide on the carrier made of γ-alumina.

In this embodiment, the reforming of ethanol is performed in exactly the same manner as in Embodiment 1, except that the temperature detected by the temperature sensor 51a provided on the outlet side of the fuel reformer 51 is 450 ° C. went. Then, after continuously operating the fuel reformer 1 for 100 hours, the fuel reforming catalyst was taken out, and the amount of carbon deposited on the fuel reforming catalyst was measured. The results are shown in Table 1 as a ratio of mass to carrier.
[Comparative Example 2]
In this comparative example, the amount of carbon deposited on the ruthenium catalyst was measured in exactly the same manner as in Example 2 except that the same commercially available ruthenium catalyst as that used in Comparative Example 1 was used. The results are shown in Table 1 as the ratio of mass to carrier.

  From Table 1, according to the fuel reforming catalyst of the present invention, carbon support can be suppressed even in a lower temperature range than before by supporting 10% by mass of cerium oxide on the support made of γ-alumina. it is obvious.

  In this embodiment, the fuel reformer 1 shown in FIG. 1 is used to reform each fuel of city gas, ethanol, gasoline, kerosene, and light oil, and the temperature at which the conversion rate becomes 99% or more is changed to the fuel reformer. This was detected by a temperature sensor 51a provided on the outlet side of the mass device 51. Each fuel was desulfurized in advance and the sulfur concentration was 200 ppb or less. The results are shown in Table 2.

  From Table 2, according to the fuel reforming catalyst of the present invention, by supporting 10% by mass of cerium oxide on the carrier made of γ-alumina, the temperature at which the conversion becomes 99% or more is 500 ° C. It is clear that the low temperature activity of the ruthenium catalyst is improved.

In this example, a fuel reforming catalyst was produced in exactly the same way as in Example 1 except that part of cerium oxide was replaced with zirconium oxide (ZrO ₂ ). Zirconium oxide was varied in the range of 0 to 70% by mass.

  Next, using the various fuel reforming catalysts obtained in this example, the temperature detected by the temperature sensor 51a provided on the outlet side of the fuel reformer 51 was set to 450 ° C. Kerosene was reformed in exactly the same manner as in Example 1, and the fuel conversion rate was calculated. The results are shown in Table 3.

  Further, kerosene was reformed in the same manner as in Example 2 except that various fuel reforming catalysts obtained in this example were used, and the amount of carbon deposited on each fuel reforming catalyst was measured. . The results are shown in Table 3 as a ratio of mass to carrier.

  From Table 3, according to the fuel reforming catalyst of the present invention in which 10 to 20% by mass of cerium oxide is substituted with zirconium oxide, an excellent fuel conversion rate can be obtained as compared with the case outside the above range, and carbon It is apparent that the durability of the catalyst can be improved by suppressing the precipitation of the catalyst.

  DESCRIPTION OF SYMBOLS 1 ... Fuel reformer, 2 ... Fuel supply part, 3 ... Water vapor generation part, 4 ... Water / fuel mixing part, 5 ... Fuel reforming part, 6 ... Wet flow meter, 7 ... Fourier-transform infrared spectrometer 8 ... Gas chromatograph apparatus.

Claims (4)

A fuel reforming catalyst in which a noble metal catalyst is supported on a carrier made of γ-alumina,
A fuel reforming catalyst comprising 5 to 30% by mass of cerium oxide supported on the carrier.   2. The fuel reforming catalyst according to claim 1, wherein the noble metal is ruthenium. 3. The fuel reforming catalyst according to claim 1, wherein the γ-alumina has a specific surface area in the range of 100 to 300 m ² / g and a fine surface area in the range of 0.2 to 0.7 cm ³ / g. A fuel reforming catalyst comprising a pore volume and a packing density in the range of 0.4 to 0.9 g / cm ³ .   The fuel reforming catalyst according to any one of claims 1 to 3, wherein 10 to 20% by mass of the cerium oxide is substituted with zirconium oxide.

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