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EP0872911A2 - Absorberschicht für einen mit Hochfrequenz beheizbaren Katalysator - Google Patents

Absorberschicht für einen mit Hochfrequenz beheizbaren Katalysator Download PDF

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Publication number
EP0872911A2
EP0872911A2 EP98106509A EP98106509A EP0872911A2 EP 0872911 A2 EP0872911 A2 EP 0872911A2 EP 98106509 A EP98106509 A EP 98106509A EP 98106509 A EP98106509 A EP 98106509A EP 0872911 A2 EP0872911 A2 EP 0872911A2
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EP
European Patent Office
Prior art keywords
frequency
catalyst
metal oxide
absorbing layer
frequency heating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP98106509A
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English (en)
French (fr)
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EP0872911A3 (de
Inventor
Katsumi Takatsu
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Bosch Corp
Original Assignee
Zexel Corp
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Priority claimed from JP9097595A external-priority patent/JPH10286468A/ja
Priority claimed from JP9100530A external-priority patent/JPH10288027A/ja
Application filed by Zexel Corp filed Critical Zexel Corp
Publication of EP0872911A2 publication Critical patent/EP0872911A2/de
Publication of EP0872911A3 publication Critical patent/EP0872911A3/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
    • H05B6/105—Induction heating apparatus, other than furnaces, for specific applications using a susceptor
    • H05B6/108—Induction heating apparatus, other than furnaces, for specific applications using a susceptor for heating a fluid

Definitions

  • the present invention relates to a high-frequency heating catalyst used in an exhaust gas apparatus for an internal combustion engine or the like and, particularly, to a high-frequency heating catalyst for making clean harmful exhaust gas exhausted at the time of the start of the engine at low temperatures.
  • Exhaust gas from a car contains air pollutants such as hydrocarbon, carbon monoxide and nitrogen oxide.
  • air pollutants such as hydrocarbon, carbon monoxide and nitrogen oxide.
  • the post-processing system using a catalyst comprises letting exhaust gas from a car pass through cleaning means having a three-element catalyst composed of a precious metal element alloy such as Pd/Rh or Pt/Rh to oxide hydrocarbon and carbon monoxide and reduce nitrogen oxide so as to change them into harmless carbonate gas, vapor and nitrogen and discharging them from the car.
  • the cleaning means 23A comprises a substrate 1 which has a honeycomb structure and is made from a ceramic material such as alumina which rarely absorbs a high-frequency wave and a high-frequency heating catalyst 2A formed on the barrier 1K of the substrate 1 and having a three-element catalyst 2b such as Pd/Rh or Pt/Rh carried on a high-frequency absorbing material 2a such as ZnO which absorbs a microwave.
  • the high-frequency absorbing material 2a converts the energy of the microwave radiation into heat energy to raise the temperature of the catalyst 2b to its operation temperature, thereby removing harmful substances contained in exhaust gas passing through through holes 1S in the substrate 1.
  • Figs. 10(a) and 10(b) are diagrams showing the structure of conventionally used cleaning means 23B which comprises (1) a substrate 1 composed of an insulating cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance and (2) a high-frequency heating catalyst 2B which comprises a high-frequency absorbing layer 2c formed on the surface of each barrier 1K of the substrate 1 and made from a high-frequency absorbing material and a wash coat layer 2d formed on the surface of the high-frequency absorbing layer 2c and carrying Pt/Rh dispersed therein.
  • the Pt/Rh catalyst is dispersed and carried in the vicinity of the surface of the wash coat layer 2d.
  • a microwave irradiated onto the cleaning means 23B is converted into heat by the above high-frequency absorbing layer 2c to raise the temperature of Pt/Rh dispersed and carried in the vicinity of the surface of the wash coat layer 2d to its operation temperature, whereby harmful substances contained in the exhaust gas passing through the cleaning means 23B are removed.
  • the heat capacity of the wash coat layer 2d is large in the cleaning means 23B, the power of the input microwave must be made large to quickly heat Pt/Rh (catalyst) dispersed and carried in the vicinity of the surface of the wash coat layer 2d.
  • the cleaning means 23A since the high-frequency heating catalyst 2A is a mixture of a high-frequency absorbing material 2a and a three-element catalyst 2b, the heat propagation efficiency thereof is higher than that of the high-frequency heating catalyst 2B.
  • the impedances of the high-frequency heating catalysts 2A and 2B do not match the characteristic impedance of the propagation space. Therefore, when the conventional high-frequency heating catalysts 2A and 2B are used, a high-frequency wave is reflected on the surfaces of the high-frequency heating catalysts 2A and 2B, thereby greatly reducing the absorption efficiency of the high-frequency wave.
  • the conventional high-frequency heating catalyst 2A which is a mixture of a high-frequency absorbing material 2a such as ZnO or CoO and a three-element catalyst 2b
  • the content of the three-element catalyst 2b must be increased.
  • the heating efficiency of the high-frequency heating catalyst 2A lowers.
  • the high-frequency heating catalysts 2A and 2B are carried on the surface or in the interior of the substrate 1 uniformly and a flow direction of the exhaust gas G is not taken into account, efficient high-frequency heating is impossible.
  • La (1-x) Sr x CoO 3 containing Co is used as the high-frequency absorbing material in conjunction with with the substrate 1 composed of a cordierite sintered body which is a composite metal oxide essentially composed of MgO and Al2O3, Al contained in the substrate 1 reacts with Co contained in the high-frequency absorbing layer 2c upon a rise in the temperature of the high-frequency heating catalyst 2B with the result that the composition ratio of the La(1-x)SrxCoO3 differs from the initial composition ratio, thereby deteriorating the heat conversion efficiency of the microwave. As a result, the temperature elevation rate of the catalyst lowers and the catalytic function efficiency of the high-frequency heating catalyst 2B deteriorates.
  • the high-frequency absorbing material contains Mn like La(1-x)SrxMnO3 and the material forming the substrate 1 contains Si like a composite oxide of SiO2 and MgO, the same reaction occurs with the result of a reduction in the catalytic function efficiency of the high-frequency heating catalyst 2B.
  • a high-frequency heating catalyst which comprises a high-frequency absorbing layer formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from a high-frequency absorbing material and a catalyst such as Pd, Pd/Rh or Pt/Rh, carried by the high-frequency absorbing layer, for making clean harmful substances contained in exhaust gas, wherein the high-frequency absorbing layer is made from a mixture of an electroconductive metal oxide and an insulating material having an impedance adjusted to the characteristic impedance of a medium through which a high-frequency wave is transmitted such that reflection power ratio becomes 10 dB or more.
  • a high-frequency heating catalyst wherein the insulating material is a metal oxide having co-catalytic activity such as ceria or ceria stabilized zirconia.
  • a high-frequency heating catalyst wherein the insulating material is a metal oxide having a large specific surface area such as g-alumina.
  • a high-frequency heating catalyst which comprises a catalyst carrying layer, formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from either one or both of a metal oxide having co-catalytic activity and a metal oxide material having a large specific surface area, which a catalyst material such as Pd, Pd/Rh or Pt/Rh for making clean harmful substances contained in exhaust gas is uniformly dispersed in and carried by, and a high-frequency absorbing layer formed on part of the surface of the catalyst carrying layer and made from a mixture of an insulating material and an electroconductive metal oxide, wherein the high-frequency absorbing layer is formed on an upstream side of exhaust gas to be cleaned.
  • a high-frequency heating catalyst wherein the insulating material contains either one or both of a metal oxide having co-catalytic activity and a metal oxide material having a large specific surface area, which a catalyst such as Pd, Pd/Rh or Pt/Rh for making clean harmful substances contained in exhaust gas is uniformly dispersed in and carried by.
  • a high-frequency heating catalyst which comprises a wash coat layer formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from a heat resistant material such as g-alumina or ceria stabilized zirconia having a large specific surface area, and a high-frequency absorbing layer formed on part of the surface of the wash coat layer and made from a mixture of an electroconductive metal oxide and an insulating material and which has a catalyst such as Pt, Pt/Rh or Pd/Rh for making clean harmful substances contained in exhaust gas carried on the surfaces or in the vicinity of the surfaces of the wash coat layer and the high-frequency absorbing layer, wherein the high-frequency absorbing layer is formed on an upstream side of exhaust gas to be cleaned.
  • a high-frequency heating catalyst wherein the high-frequency absorbing layer contains a co-catalyst material such as ceria or ceria stabilized zirconia having co-catalytic activity and g-alumina or ceria stabilized zirconia having a large specific surface area.
  • a co-catalyst material such as ceria or ceria stabilized zirconia having co-catalytic activity and g-alumina or ceria stabilized zirconia having a large specific surface area.
  • a high-frequency heating catalyst wherein the material having co-catalytic activity and the heat resistant material do not contain an element which reacts with a metal element contained in the electroconductive metal oxide.
  • a high-frequency heating catalyst wherein an intermediate layer made from a metal oxide which does not contain a component reacting with a metal element component contained in the high-frequency absorbing layer at high temperatures is formed between the high-frequency absorbing layer and the substrate.
  • a high-frequency heating catalyst wherein when an electroconductive metal oxide containing Co is used as a high-frequency absorbing material, a metal oxide containing no Al, such as SiO2, ZrO2 or CeO2, or a composite metal oxide of two or more thereof is used to form the intermediate layer.
  • a high-frequency heating catalyst wherein when an electroconductive metal oxide containing Mn is used as a high-frequency absorbing material, a metal oxide containing no Si, such as CaO, Al 2 O 3 or CeO 2 , or a composite metal oxide of two or more thereof is used to form the intermediate layer.
  • a metal oxide containing no Si such as CaO, Al 2 O 3 or CeO 2
  • a composite metal oxide of two or more thereof is used to form the intermediate layer.
  • Figs. 1(a), 1(b) and 1(c) are diagrams showing the structure of exhaust gas cleaning means 23 according to Embodiment 1 of the present invention.
  • the cleaning means 23 comprises (1) a substrate 1 composed of a cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance and (2) a high-frequency heating catalyst 2 coated on the surface of each barrier 1K of the substrate 1.
  • reference symbol 1s denotes through holes formed in the substrate 1.
  • exhaust gas G is made clean by the high-frequency heating catalyst 2 while it passes through the through holes 1s in the cleaning means 23 and discharged.
  • the high-frequency catalyst 2 has Pt/Rh, a three-element catalyst, carried by a high-frequency absorbing layer made from a mixture of La 0.6 Sr 0.4 MnO 3 which is an electroconductive metal oxide and ceria stabilized zirconia which is an insulating material having co-catalytic activity and a large specific surface area.
  • the mixing ratio of the electroconductive metal oxide and the insulating material is controlled to adjust the impedance of the high-frequency absorbing layer to the characteristic impedance of a transmission path through which a high-frequency wave is transmitted such that reflection power ratio becomes 10 dB or more at an oscillation frequency of a microwave.
  • the high-frequency absorbing layer is coated on the substrate 1 and then heated to be firmly fixed to the barrier 1K of the substrate 1.
  • the Pt/Rh three-element catalyst is carried on the surface or in the interior of the high-frequency absorbing layer by immersing the substrate 1 having the high-frequency absorbing layer formed thereon in a solution containing Pt/Rh and heating it. Since ceria stabilized zirconia which is an insulating material contained in the high-frequency absorbing layer has a large specific surface area, the Pt/Rh catalyst can be uniformly dispersed into the high-frequency absorbing layer.
  • Fig. 2 is a diagram showing the constitution of an exhaust gas cleaning apparatus equipped with the cleaning means 23 having the above high-frequency heating medium 2.
  • a microwave generated by a high-frequency oscillator 25 passes through a waveguide path 26 and is transmitted to a cylindrical heating chamber 22 (cavity) whose impedance is adjusted to the impedance of the waveguide path 26 in a joint slot 28.
  • the exhaust gas G is guided from an exhaust pipe 21 into the heating chamber 22 and discharged from an exhaust pipe 21b.
  • Reflection plates 27a and 27b made from a punching metal are installed at both ends of the heating chamber 22, and the inner diameter and length of the heating chamber 22 are designed such that a microwave resonates in the heating chamber 22.
  • Reflection plates 27a and 27b made from a punching metal are installed at both ends of the heating chamber 22, and the inner diameter and length of the heating chamber 22 are designed such that a microwave resonates in the heating chamber 22.
  • reference letter P indicates the field strength of a standing wave in the heating chamber 22, and the high-frequency heating medium 2 is held by a supporting member 24 at a position of ⁇ g/4 ( ⁇ g is a wavelength in the waveguide) from the reflection plate 27b installed on a downstream side of exhaust gas G in the heating chamber 22, that is, a position where the amplitude of the standing wave is maximum.
  • the material of the high-frequency heating catalyst 2 is designed to adjust the impedance of the high-frequency absorbing layer of the high-frequency heating catalyst 2 to the characteristic impedance of the propagation path of the heating chamber 22 as described above, the reflection of a microwave by the cleaning means 23 is small and the energy of the microwave irradiated onto the high-frequency heating catalyst 2 is absorbed by the high-frequency absorbing layer efficiently. Therefore, the temperature of the catalyst contained in the high-frequency heating catalyst 2 can be sharply increased, the temperature of the catalyst can be raised to its operation temperature quickly even at the time of the start of an internal combustion engine at low temperatures, and harmful exhaust gas exhausted at the time of start at low temperatures can be made clean.
  • the impedance of the high-frequency absorbing layer in the high-frequency heating catalyst 2 is adjusted to the characteristic impedance of the propagation path through which a microwave is transmitted such that reflection power ratio becomes 10 dB or more at an oscillation frequency of the microwave. Therefore, the reflection of the microwave by the high-frequency absorbing layer is small, the temperature of the catalyst can be raised sharply, and the temperature of the catalyst can be increased to its operation temperature quickly even at the time of the start of an internal combustion engine at low temperatures, thereby making it possible to make clean harmful exhaust gas exhausted at the time of start at low temperatures.
  • ceria stabilized zirconia which is an insulating material contained in the high-frequency heating catalyst 2 has co-catalytic activity and a large specific surface area, the catalytic function of the Pt/Rh catalyst is improved, whereby the cleaning function of the harmful exhaust gas of the catalyst can be enhanced.
  • ceria stabilized zirconia is used as the insulating material.
  • a metal oxide having a high specific surface area such as ⁇ -alumina having a large specific surface area and ceria having co-catalytic activity is used, the same effect as above is obtained.
  • the Pt/Rh catalyst is carried on the surface or in the interior of the high-frequency absorbing layer.
  • a slurry of a mixture of the above electroconductive metal oxide and the insulating material is mixed with a solution containing a catalyst such as Pt/Rh and stirred to prepare a solution and the solution is coated on the substrate 1 to form the high-frequency heating catalyst 2
  • the catalyst such as Pt/Rh is uniformly dispersed into the high-frequency absorbing material. Therefore, the catalytic function of the high-frequency heating catalyst 2 can be further improved.
  • Fig. 3 is a diagram showing the structure of exhaust gas cleaning means 23 according to Embodiment 2 of the present invention.
  • the cleaning means 23 comprises (1) a substrate 1 composed of a cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance, and (2) a high-frequency heating catalyst 2 formed on the surface of each barrier 1K of the substrate 1.
  • the high-frequency heating catalyst 2 comprises a first catalyst carrying layer 3 comprising ceria stabilized zirconia and a Pd/Rh catalyst, and a second catalyst carrying layer 4, formed on part of the surface of the fist catalyst carrying layer 3, which is a high-frequency absorbing layer comprising La 0.6 Sr 0.4 MnO 3 and ceria stabilized zirconia having co-catalytic ability and a Pd catalyst.
  • the second catalyst carrying layer 4 is formed on an upstream side of exhaust gas G to be cleaned.
  • the second catalyst carrying layer 4 is formed by preparing a slurry comprising La 0.6 Sr 0.4 MnO 3 , an electroconductive metal oxide, and ceria stabilized zirconia, an insulating material, whose mixing ratio is controlled to adjust the impedance of the second catalyst carrying layer 4 to the characteristic impedance of a transmission path through which a high-frequency wave is transmitted such that reflection power ratio becomes 10 dB or more and dip coating the slurry on the first catalyst carrying layer 3.
  • the second catalyst carrying layer 4 can be formed on only one side of the substrate 1 by immersing only one side of the substrate 1 into the slurry.
  • the cleaning means 23 comprising the above high-frequency heating catalyst 2 was installed in an exhaust gas cleaning apparatus as shown in Fig. 2 like the above Embodiment 1, exhaust gas from an internal combustion engine while idling was caused to flow through the apparatus, and the cleaning means 23 was irradiated with a microwave generated from the high-frequency oscillator 25 and having an output power of 800 W and a frequency of 2.45 GHz.
  • the cleaning means 23A having the conventional high-frequency heating catalyst 2B was used, it took about 20 seconds to increase the surface temperature of the high-frequency heating catalyst 2B to its reaction start temperature (about 300°C).
  • the reflection of a microwave by the cleaning means 23 is little and the energy of a microwave irradiated onto the high-frequency heating catalyst 2 is efficiently absorbed by the second catalyst carrying layer 4 which is a high-frequency absorbing layer as the material of the high-frequency heating catalyst 2 is designed to adjust the impedance of the second catalyst carrying layer 4 which is a high-frequency absorbing layer to the characteristic impedance of the propagation path in the heating chamber 22 such that reflection power ratio becomes 10 dB or more.
  • the temperature of the supplied exhaust gas G rises and catalysts on a downstream side out of the catalysts contained in the cleaning means 23 are heated by the supplied exhaust gas G, thereby advancing the start time of a catalytic reaction.
  • the second catalyst carrying layer 4 contains ceria stabilized zirconia having co-catalytic activity and the Pd catalyst, heat is generated by the catalytic reaction in the front of the high-frequency heating catalyst 2 at the same time. Therefore, the temperature of the supplied exhaust gas G rises higher than when only the high-frequency absorbing layer is formed at the front of the cleaning means 23, thereby further quickening a rise in the temperature of the catalyst.
  • ceria stabilized zirconia is used as the insulating material for the first catalyst carrying layer 3.
  • the first catalyst carrying layer 3 may be formed by containing a catalyst such as Pt/Rh or Pd/Rh in ⁇ -alumina or a mixture of ⁇ -alumina and ceria.
  • Ceria stabilized zirconia is used as the insulating material contained in the second catalyst carrying layer 4.
  • a metal oxide such as a mixture of ⁇ -alumina having co-catalytic activity and a large specific surface and ceria is used as the insulating material, the same effect is obtained.
  • the start time of the catalytic reaction can be advanced even when a high-frequency absorbing layer composed of an insulating material and an electroconductive metal oxide is formed on an upstream side of exhaust gas in place of the second catalyst carrying layer 4 because the front of the high-frequency heating catalyst 2 is heated efficiently, the temperature of exhaust gas G rises, and catalysts on a downstream of the cleaning means are heated by the exhaust gas G.
  • Fig. 4 is a diagram showing the structure of exhaust gas cleaning means 23 according to Embodiment 3 of the present invention.
  • the cleaning means 23 comprises (1) a substrate 1 composed of a cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance, and (2) a high-frequency heating catalyst 2 formed on the surface of each barrier 1K of the substrate 1.
  • the high-frequency heating catalyst 2 comprises a wash coat layer 5 made from ceria stabilized zirconia, a high-frequency absorbing layer 6, formed on part of the surface of the wash coat layer, comprising La 0.6 Sr 0.4 MnO 3 and ceria stabilized zirconia, and a catalyst layer 7 formed from Pd/Rh carried in the vicinity of the surfaces of the wash coat layer 5 and the high-frequency absorbing layer 6.
  • the high-frequency absorbing layer 6 is formed on an upstream side of exhaust gas G to be cleaned.
  • the above high-frequency absorbing layer 6 is formed by preparing a slurry comprising La 0.6 Sr 0.4 MnO 3 , an electroconductive metal oxide, and ceria stabilized zirconia, an insulating material, whose mixing ratio is controlled to adjust the impedance of the high-frequency absorbing layer 6 to the characteristic impedance of a transmission path through which a high-frequency wave is transmitted such that reflection power ratio becomes 10 dB or more and dip coating the slurry on the wash coat layer 5.
  • the high-frequency absorbing layer 6 can be formed on only one side of the substrate 1 by immersing only one side of the substrate 1 into the slurry.
  • the catalyst layer 7 is carried on the surfaces and in the interiors of the surfaces of the wash coat layer 5 and the high-frequency absorbing layer 6 by immersing the substrate 1 having the wash coat layer 5 and the high-frequency absorbing layer 6 formed thereon in a solution containing Pd/Rh and heating. Since ceria stabilized zirconia which is an insulating material contained in the high-frequency absorbing layer 6 has a large specific surface area, the Pd/Rh catalyst is carried by the high-frequency absorbing layer 6 in high concentration.
  • the cleaning means 23 comprising the above high-frequency heating catalyst 2 was installed in an exhaust gas cleaning apparatus as shown in Fig. 2 like the above Embodiment 1, exhaust gas from an internal combustion engine while idling was caused to flow through the apparatus, and the cleaning means 23 having a diameter of 90 mm and a length of 30 mm was irradiated with a microwave generated from the high-frequency oscillator 25 and having an output power of 800 W and a frequency of 2.45 GHz.
  • the cleaning means 23B having the conventional high-frequency heating catalyst 2B was used, it took about 20 seconds to increase the surface temperature of the high-frequency heating catalyst 2B to its catalytic reaction start temperature (about 300°C).
  • the start time of a catalytic reaction can be advanced. Further, since the Pd/Rh catalyst is carried in the vicinity of the surface of the high-frequency absorbing layer 6 in high concentration, a large amount of heat is generated by the catalytic reaction at the same time, thereby making it possible to further quicken a rise in the temperature of the catalyst. Further, since the use efficiency of the catalyst is high, the amount of a precious metal used in the catalyst can be reduced.
  • ceria stabilized zirconia is used as the insulating material for the wash coat layer 5.
  • ⁇ -alumina or a mixture of ⁇ -alumina and ceria may be used.
  • La 0.6 Sr 0.4 MnO 3 is used as the high-frequency absorbing material.
  • a composite metal oxide such as La (1-x) Sr x CoO 3 , La (1-x) Sr x CrO 3 , La (1-x) Sr x MnO 3 , La (1-x) Sr x Co (1-y) Pd y O 3 , La (1-x) Sr x Mn (1-y) Pd y O 3 , La (1-x) Ca x CoO 3 or La (1-x) Ca x MnO 3 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1) or a mixture thereof is used, the same effect is obtained.
  • the material forming the layer in contact with the layer containing the above high-frequency absorbing material for example, the first catalyst carrying layer 3 of the above Embodiment 2 or the wash coat layer 5 of the above Embodiment, is a compound containing Si, Mn and Si react with each other at high temperatures with the result that the impedance of the high-frequency absorbing material forming the second catalyst carrying layer 4 or the high-frequency absorbing layer 6 changes, thereby greatly reducing the microwave absorption efficiency of the high-frequency heating catalyst 2.
  • the electroconductive metal oxide contains Co
  • the layer in contact with the layer containing the high-frequency absorbing material must be composed of a compound containing no Al.
  • La 0.6 Sr 0.4 MnO 3 is used as the high-frequency absorbing material and ceria stabilized zirconia is used as the material forming the second catalyst carrying layer 4 in the above Embodiment 2, even if the surface temperature of the cleaning means 23 rises, the above reaction does not occur and a change in the catalytic activity of the high-frequency heating catalyst 2 is not observed. Since La 0.6 Sr 0.4 MnO 3 is used as the high-frequency absorbing material and ceria stabilized zirconia is used as the material forming the wash coat layer 5 in the above Embodiment 3, even if the surface temperature of the cleaning means 23 rises, a change in the catalytic activity of the high-frequency heating catalyst 2 is not observed.
  • Figs. 5(a) to 5(d) are diagrams showing the structure of exhaust gas cleaning means 23 according to Embodiment 4 of the present invention.
  • Fig. 5(a) is a diagram showing the outer appearance
  • Fig. 5(b) is a sectional view
  • Fig. 5(c) is a partially enlarged front view of the cleaning means 23.
  • Fig. 5(d) is a diagram typically showing the layer structure of the high-frequency heating catalyst 2.
  • the cleaning means 23 comprises (1) a substrate 1 composed of a cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance, and (2) a high-frequency heating catalyst 2 which comprises an intermediate layer 8A made from ZrO 2 and coated on the surface of each barrier 1K of the substrate 1, a high-frequency absorbing layer 9A formed on the intermediate layer and made from a mixture of La 0.6 Sr 0.4 CoO 3 which is an electroconductive metal oxide and CeO 2 which is an insulating material, and a catalyst layer 10, formed on the high-frequency absorbing layer 9A and made from MgO carrying Pt/Rh.
  • a substrate 1 composed of a cordierite sintered body having a honeycomb structure, insulating properties and high thermal shock resistance
  • a high-frequency heating catalyst 2 which comprises an intermediate layer 8A made from ZrO 2 and coated on the surface of each barrier 1K of the substrate 1, a high-frequency absorbing layer 9A formed on the intermediate layer and made from a mixture of La 0.6 Sr 0.4 Co
  • the above-structured cleaning means 23 was installed in the heating chamber 22 of an exhaust gas cleaning apparatus as shown in Fig. 2 and irradiated with a microwave generated from the high-frequency oscillator 25 and having an output power of 600 W and a frequency of 2.45 GHz, the surface temperature of the high-frequency heating catalyst 2 reached about 800°C in 30 seconds due to the energy of the microwave and heat generated by a catalytic reaction.
  • the properties of the high-frequency absorbing layer 9A of the high-frequency heating catalyst 2 did not change and the temperature rise characteristics of the high-frequency heating catalyst 2 hardly changed even when its surface temperature was raised to about 800°C repeatedly under the above conditions. Further, the electric resistance of the high-frequency absorbing layer 9A did not change after the repeated temperature rise test.
  • Fig. 6 is a diagram showing the structure of the high-frequency heating catalyst 2 having a high-frequency absorbing layer made from an electroconductive metal oxide containing Mn.
  • the high-frequency heating catalyst 2 comprises an intermediate layer 8B formed on the barrier 1K of the substrate 1 composed of a cordierite sintered body and made from Al 2 O 3 , a high-frequency absorbing layer 9B formed on the intermediate layer 8B and made from a mixture of La 0.6 Sr 0.4 MnO 3 which is an electroconductive metal oxide and CeO 2 which is an insulating material, and a catalyst layer 10, formed on the high-frequency absorbing layer 9B and made from MgO carrying Pt/Rh.
  • the material forming the high-frequency absorbing layer 9A is La 0.6 Sr 0.4 CoO 3 containing Co, ZrO 2 , a metal oxide containing no Al, is used to form the intermediate layer 8A between the high-frequency absorbing layer 9A and the substrate 1.
  • the material forming the high-frequency absorbing layer 9B is La 0.6 Sr 0.4 MnO 3 containing Mn, Al 2 O 3 , a metal oxide containing no Si is used to form the intermediate layer 8B.
  • the high-frequency heating catalyst 2 is heated to about 800°C by microwave radiation, the properties of La 0.6 Sr 0.4 CoO 3 or La 0.6 Sr 0.4 MnO 3 forming the high-frequency absorbing layer (9A or 9B) do not change and hence, the catalytic function of the high-frequency heating catalyst 2 does not deteriorate.
  • the catalyst layer 22A or 22B is formed on the high-frequency absorbing layer 9A or 9B in the above Embodiment 4, and the intermediate layer 8A or 8B is formed between the substrate 1 and the high-frequency absorbing layer 9A or 9B. As shown in Fig.
  • the high-frequency heating catalyst having a high-frequency absorbing layer 9C made from a high-frequency absorbing material carrying a catalyst such as Pt/Rh, ZrO 2 ,a metal oxide containing no Al is used to form an intermediate layer 8C between the barrier 1K of the substrate 1 and the high-frequency absorbing layer 9C when the material forming the high-frequency absorbing layer 9C is La 0.6 Sr 0.4 CoO 3 containing Co, and Al 2 O 3 , a metal oxide containing no Si, is used to form the intermediate layer 8C when the material forming the high-frequency absorbing layer 9C is La 0.6 Sr 0.4 MnO 3 containing Mn.
  • La 0.6 Sr 0.4 CoO 3 containing Co or La 0.6 Sr 0.4 MnO 3 containing Mn is used as the material forming the high-frequency absorbing layer.
  • La (1-x) Sr x CoO 3 , La (1-x) Sr x CrO 3 , La (1-x) Sr x MnO 3 , La (1-x) Sr x Co (1-y) Pd y O 3 or La (1-x) Sr x Mn (1-y) Pd y O 3 (0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1) may be used.
  • the intermediate layer may be made from a metal oxide such as MgO, SiO 2 , CaO or CeO 2 , or a composite oxide of two or more thereof in addition to the above ZrO 2 .
  • MgO, ZrO 2 , CaO or CeO 2 , or a composite metal oxide of two or more thereof may be used as the metal oxide containing no Si in addition to the above Al 2 O 3 .
  • the high-frequency heating catalyst according to the first aspect of the present invention comprises a high-frequency absorbing layer formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from a high-frequency absorbing material and a catalyst such as Pd, Pd/Rh or Pt/Rh, carried by the high-frequency absorbing layer, for making clean harmful substances contained in exhaust gas, and the high-frequency absorbing layer is made from a mixture of an electroconductive metal oxide and an insulating material having an impedance adjusted to the characteristic impedance of a medium through which a high-frequency wave is transmitted such that reflection power ratio becomes 10 dB or more.
  • the reflection of high-frequency radiation is little, the high-frequency wave can be absorbed and converted into heat energy effectively, and the temperature of the catalyst can be thereby increased to its operation temperature quickly at the time of the start of an internal combustion engine at low temperatures.
  • harmful exhaust gas exhausted at the time of the start at low temperatures can be made clean.
  • the insulating material is a metal oxide having co-catalytic activity such as ceria. Therefore, the catalytic function of the high-frequency heating catalyst can be further improved.
  • the insulating material is a metal oxide having a large specific surface area such as ceria stabilized zirconia. Therefore, a catalyst such as Pd, Pd/Rh or Pt/Rh can be uniformly carried by the high-frequency absorbing layer, and differences in the function of the high-frequency catalyst at different sites can be eliminated.
  • the high-frequency heating catalyst according to the fourth aspect of the present invention comprises a catalyst carrying layer, formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from either one or both of a metal oxide having co-catalytic activity and a metal oxide material having a large specific surface area, which a catalyst material such as Pd, Pd/Rh or Pt/Rh for making clean harmful substances contained in exhaust gas is uniformly dispersed in and carried by, and a high-frequency absorbing layer formed on part of the surface of the catalyst carrying layer and made from a mixture of an insulating material and an electroconductive metal oxide, and the high-frequency absorbing layer is formed on an upstream side of exhaust gas to be cleaned. Therefore, since exhaust gas heated at an upstream heats a downstream portion of the high-frequency heating catalyst, the temperature of the catalyst can be increased to its operation temperature quickly.
  • the insulating material contains either one or both of a metal oxide having co-catalytic activity and a metal oxide material having a large specific surface area, which a catalyst such as Pd, Pd/Rh or Pt/Rh for making clean harmful substances contained in exhaust gas is uniformly dispersed in and carried by. Therefore, the exhaust gas is further heated by a catalyst reaction in the high-frequency absorbing layer at an upstream, thereby making it possible to increase the temperature of the catalyst to its operation temperature more quickly.
  • the high-frequency heating catalyst according to the sixth aspect of the present invention comprises a wash coat layer formed on the surface of a substrate made from a material which rarely absorbs a high-frequency wave and made from a heat resistant material such as ⁇ -alumina or ceria stabilized zirconia having a large specific surface area, and a high-frequency absorbing layer formed on part of the surface of the wash coat layer and made from a mixture of an electroconductive metal oxide and an insulating material, a catalyst such as Pt, Pt/Rh or Pd/Rh for making clean harmful substances contained in exhaust gas is carried on the surfaces or in the vicinity of the surfaces of the wash coat layer and the high-frequency absorbing layer, and the high-frequency absorbing layer is formed on an upstream side of exhaust gas to be cleaned. Therefore, the exhaust gas at an upstream is also heated by heat generated by a catalytic reaction, thereby making it possible to increase the temperature of the catalyst to its operation temperature more quickly.
  • a catalyst such as Pt, Pt/Rh or Pd/R
  • the high-frequency absorbing layer contains a co-catalyst material such as ceria or ceria stabilized zirconia having co-catalytic activity and ⁇ -alumina or ceria stabilized zirconia having a large specific surface area. Therefore, the catalytic function of the high-frequency heating catalyst can be further improved.
  • the material having co-catalytic activity and the heat resistant material do not contain an element which reacts with a metal element contained in the electroconductive metal oxide. Therefore, the high-frequency catalyst can be used at a wide temperature range.
  • an intermediate layer made from a metal oxide which does not contain a component reacting with a metal element component contained in the high-frequency absorbing layer at high temperatures is formed between the high-frequency absorbing layer and the substrate. Therefore, even when the high-frequency absorbing material is heated to a high temperature by the absorption of a microwave, a reaction does not occur between the material forming the high-frequency absorbing layer and the material forming the substrate and the catalyst function does not deteriorate. Further, since there are no changes in the characteristics of the high-frequency heating catalyst after long-term use, the reliability of the high-frequency heating catalyst can be greatly improved.
  • the high-frequency heating catalyst when the high-frequency absorbing layer is made from a material containing Co, a metal oxide containing no Al is used to form the intermediate layer. Therefore, the composition of the intermediate layer can be limited in advance.
  • the high-frequency heating catalyst according to the eleventh aspect of the present invention when the high-frequency absorbing layer is made from a material Containing Mn, a metal oxide containing no Si is used to form the intermediate layer. Therefore, the composition of the intermediate layer can be limited in advance.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Catalysts (AREA)
EP98106509A 1997-04-15 1998-04-08 Absorberschicht für einen mit Hochfrequenz beheizbaren Katalysator Withdrawn EP0872911A3 (de)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
JP97595/97 1997-04-15
JP9759597 1997-04-15
JP9097595A JPH10286468A (ja) 1997-04-15 1997-04-15 高周波加熱触媒及び高周波吸収体
JP10053097 1997-04-17
JP100530/97 1997-04-17
JP9100530A JPH10288027A (ja) 1997-04-17 1997-04-17 高周波加熱触媒

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EP0872911A2 true EP0872911A2 (de) 1998-10-21
EP0872911A3 EP0872911A3 (de) 2000-05-03

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1160427A3 (de) * 2000-05-31 2002-11-06 Corning Incorporated Partikelfilter für Dieselbrennkraftmaschinen
EP1160426A3 (de) * 2000-05-31 2002-11-06 Corning Incorporated Partikelfilter für Dieselbrennkraftmaschinen
KR20020094720A (ko) * 2001-06-13 2002-12-18 현대자동차주식회사 디젤자동차 입자상 물질 제거용 촉매 및 그 제조방법
WO2003033883A1 (en) * 2001-10-17 2003-04-24 UNIVERSITEIT VAN AMSTERDAM Department of Chemical Engineering Regenerative soot filter device and method for regenerating a soot filter
US7981389B2 (en) * 2005-01-31 2011-07-19 Toyota Motor Corporation Process using microwave energy and a catalyst to crack hydrocarbons
US20200131960A1 (en) * 2018-10-26 2020-04-30 Toyota Jidosha Kabushiki Kaisha Catalytic device and exhaust gas purification system
US20200141296A1 (en) * 2018-11-06 2020-05-07 Toyota Jidosha Kabushiki Kaisha Catalytic device and exhaust gas purification system
CN112886197A (zh) * 2021-02-10 2021-06-01 联想(北京)有限公司 一种天线组件、电子设备、天线组件的制造方法

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1160427A3 (de) * 2000-05-31 2002-11-06 Corning Incorporated Partikelfilter für Dieselbrennkraftmaschinen
EP1160426A3 (de) * 2000-05-31 2002-11-06 Corning Incorporated Partikelfilter für Dieselbrennkraftmaschinen
KR20020094720A (ko) * 2001-06-13 2002-12-18 현대자동차주식회사 디젤자동차 입자상 물질 제거용 촉매 및 그 제조방법
WO2003033883A1 (en) * 2001-10-17 2003-04-24 UNIVERSITEIT VAN AMSTERDAM Department of Chemical Engineering Regenerative soot filter device and method for regenerating a soot filter
US7981389B2 (en) * 2005-01-31 2011-07-19 Toyota Motor Corporation Process using microwave energy and a catalyst to crack hydrocarbons
US20200131960A1 (en) * 2018-10-26 2020-04-30 Toyota Jidosha Kabushiki Kaisha Catalytic device and exhaust gas purification system
US20200141296A1 (en) * 2018-11-06 2020-05-07 Toyota Jidosha Kabushiki Kaisha Catalytic device and exhaust gas purification system
US10934913B2 (en) * 2018-11-06 2021-03-02 Toyota Jidosha Kabushiki Kaisha Catalytic device and exhaust gas purification system
CN112886197A (zh) * 2021-02-10 2021-06-01 联想(北京)有限公司 一种天线组件、电子设备、天线组件的制造方法

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