JP2011036737A - Exhaust-gas catalyst for automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust-gas catalyst for an automobile which improves catalytic performance and reduces a pressure loss. <P>SOLUTION: The exhaust-gas catalyst 1 for an automobile carries a catalyst component 3 on a ceramic-made carrier 2 having a honeycomb shape. In this case, the carrier 2 is formed to be a porous material having a plurality of micropores 6, and the micropores 6 is impregnated with the catalyst component 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas catalyst for automobiles in which a catalyst component is supported on a ceramic carrier.

  Conventionally, a ceramic carrier such as cordierite or SiC has been used as a honeycomb-shaped carrier for coating a catalyst. A layer (hereinafter referred to as a WC layer) containing a catalyst component called a wash coat (hereinafter abbreviated as WC) is coated on the wall surface of the carrier. The exhaust gas from the engine comes into contact with and reacts with the WC layer so that the exhaust gas is purified.

  Further, it is known that the temperature rise rate of the exhaust gas catalyst for automobiles is increased and the purification performance is improved by making the WC layer thin (reducing weight) under the same catalyst amount condition. For example, when the honeycomb structure is molded and used with a WC layer containing a catalyst component, the purification performance is considered to be improved, but it is not suitable for practical use in terms of strength.

  Non-Patent Document 1 introduces the following equation for raising the temperature of a catalyst coated on a honeycomb-shaped carrier.

  The smaller the value of the above formula, the faster the temperature rise rate, and the more advantageous the reaction.

Japanese Patent Laid-Open No. 5-68892

Japan Society for Automotive Technology Academic Lecture Preprints No. 80-08

  When the heat of exhaust gas is used to raise the temperature of the exhaust gas catalyst as in an automobile exhaust gas catalyst, the closer to the contact surface with the exhaust gas, the more advantageous the temperature rise. A cordierite is used as a honeycomb material used for an exhaust gas catalyst for automobiles, and γ-alumina is used as a main component of WC. Comparing the thermal conductivity of the two, the thermal conductivity of γ-alumina is about 10 times greater than that of cordierite. Therefore, the relationship between the distance from the exhaust gas contact surface to the carrier, the WC concentration, and the thermal conductivity draws a downward-sloping graph as shown in FIG. As shown in FIG. 5, from the viewpoint of thermal conductivity, it is preferable to make the thickness of the WC layer 30 as thin as possible. However, a reduction in the amount of WC leads to a reduction in exhaust gas purification performance.

  For this reason, as shown in FIGS. 6 and 7, when the catalyst coating amount is increased for the purpose of improving the purification performance of the exhaust gas catalysts 34 and 35 for automobiles, the WC layers 31 and 32 become thicker and the heat transfer efficiency becomes worse. There was a problem that the catalyst performance would be degraded.

  Further, since the passage 33 through which the exhaust gas passes becomes narrow, the pressure loss before and after the exhaust gas catalysts 34 and 35 for the automobile (exhaust gas inlet and exhaust gas outlet) increases, resulting in a problem of adversely affecting the fuel consumption of the engine. It was. Furthermore, when the concentration of the catalyst component in the WC layers 31 and 32 is constant and the thickness of the WC layers 31 and 32 is large, the deep layers of the WC layers 31 and 32 (separate from the exhaust gas contact surfaces 36 and 37). There was a problem that it was unfavorable for the temperature rise of the part. For these reasons, in order to improve the purification performance of the exhaust gas catalysts 34 and 35 for automobiles, it is desirable to make the WC layers 31 and 32 thin without reducing the amount of the catalyst component. There was a problem of not doing.

  Therefore, an object of the present invention is to provide an automobile exhaust gas catalyst that can solve the above-mentioned problems, improve the catalyst performance, and reduce the pressure loss.

  In order to solve the above problems, the present invention provides an exhaust gas catalyst for automobiles in which a catalyst component is supported on a ceramic support formed in a honeycomb shape, wherein the support is formed in a porous shape having a plurality of pores, The catalyst component was impregnated in the pores.

  The porosity of the carrier is preferably 30% or more and 60% or less.

  The catalyst component may be impregnated only in the pores, and the surface of the support may be coated with another catalyst component having a composition different from that of the catalyst component.

  According to the present invention, catalyst performance can be improved and pressure loss can be reduced.

FIG. 1 is a cross-sectional view of a main part of an automobile exhaust gas catalyst showing an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part of an exhaust gas catalyst for automobiles showing another embodiment of the present invention. 3A is an enlarged cross-sectional view of the conventional carrier and the WC layer, and FIG. 3B is an enlarged cross-sectional view of the carrier and the WC layer in FIG. FIG. 4 is a graph showing the relationship between the distance from the exhaust gas contact surface, the WC concentration, and the thermal conductivity. FIG. 5 is a cross-sectional explanatory view of an automobile exhaust gas catalyst having a thin WC layer. FIG. 6 is an explanatory cross-sectional view of an automobile exhaust gas catalyst in which the catalyst coat amount is increased and the WC layer is thickened. FIG. 7 is a cross-sectional explanatory view of an automobile exhaust gas catalyst having two WC layers. FIG. 8 is an explanatory cross-sectional view of an automobile exhaust gas catalyst in which a porous carrier is coated with a WC layer.

  As shown in FIG. 1, an exhaust gas catalyst 1 for an automobile purifies exhaust gas from a diesel engine, and a catalyst component 3 is supported on a ceramic carrier 2 formed in a honeycomb shape. Specifically, the exhaust gas catalyst 1 for automobiles is a diesel oxidation catalyst (DOC) and has a function of oxidizing and removing carbon monoxide and hydrocarbons in exhaust gas by an oxidation reaction.

  The carrier 2 is formed in a honeycomb shape with cordierite, and has a plurality of parallel exhaust gas flow paths 4. The carrier 2 is formed in a porous shape having a plurality of pores 6 in the honeycomb cell wall 5 that defines the exhaust gas flow path 4. The porosity of the carrier 2 is about 50%, and the carrier 2 is formed in a substantially sponge shape.

  The catalyst component 3 is made of particles of noble metal such as platinum, and is impregnated in the pores 6 of the carrier 2 together with γ-alumina which is the main component of WC7. The carrier 2 is impregnated with the catalyst component 3 by immersing the carrier 2 in the liquid WC 7 and applying a negative pressure to the carrier 2. As shown in FIG. 3B, the impregnation depth of the WC 7 into the carrier 2 is deeper than that of the conventional automobile exhaust gas catalyst (see FIG. 3A) 8, and the thickness of the honeycomb cell wall 5 Less than half.

  Next, the operation of this embodiment will be described.

  The exhaust gas flowing into the exhaust gas flow path 4 of the automobile exhaust gas catalyst 1 comes into contact with the catalyst component 3 and reacts to be purified. At this time, since a sufficient amount of the catalyst component 3 is supported on the carrier 2, the exhaust gas can be purified with high purification performance.

  Further, since the catalyst component 3 is impregnated in the pores 6, the thickness from the surface of the WC layer 8 to the surface of the carrier 2 is thin, and the heat of the exhaust gas is transmitted to the carrier 2 well, and high catalyst performance is achieved. can get.

  And since the flow path 4 for exhaust gas in the support | carrier 2 is formed in a sufficiently large cross-sectional area, the pressure loss which arises between the exhaust gas inlet (not shown) and the exhaust gas outlet (not shown) of the exhaust gas catalyst 1 for motor vehicles. Can be kept small, and can contribute to improving the fuel consumption of the engine.

  In addition, since the voids of the carrier 2 are filled by impregnating the WC 7 in the pores 6, the strength of the automobile exhaust gas catalyst 1 is higher than when the honeycomb cell wall 5 of the carrier 2 is coated with WC 7 (see FIG. 8). Will improve.

  Thus, in the automobile exhaust gas catalyst 1 in which the catalyst component 3 is supported on the ceramic carrier 2 formed in a honeycomb shape, the carrier 2 is formed in a porous shape having a plurality of pores 6, and the catalyst component 3 is Since it is impregnated in the pores 6, the mechanical strength of the exhaust gas catalyst 1 for automobiles can be sufficiently secured, and the catalyst performance can be improved and the pressure loss can be reduced after securing the necessary amount of catalyst. Can be improved. And compared with the case where WC layer 8 is formed thickly, the usage-amount of a noble metal can be reduced and cost can be reduced. Further, the catalyst component 3 is impregnated in the pores 6 of the carrier 2 to reduce the amount of catalyst coated on the wall surface of the honeycomb cell wall 5. As a result, the weight of the exhaust gas catalyst 1 for automobile including the carrier 2 can be reduced. It can be made smaller than the conventional one, the heating rate is increased, and the purification performance is improved. Further, the pressure loss can be reduced by reducing the amount of WC7 occupying the flow path.

  Further, since the porosity of the carrier 2 is set to about 50%, the exhaust gas catalyst 1 for an automobile can be made practical strength, and the catalyst performance can be improved and the pressure loss can be reduced.

  Another embodiment will be described.

  The automobile exhaust gas catalyst 10 shown in FIG. 2 is a case where two types of catalyst components having different compositions are used. In general, oxidation catalysts and the like are often used in combination with different characteristics, and in that case, a two-layer structure is often adopted. The same components as those described above are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 2, the exhaust gas catalyst 10 for automobiles impregnates the carrier 2 with one catalyst component 11 of the two types of catalyst components having different compositions, and the other catalyst component 12 on the honeycomb cell wall. 5 is formed by coating the wall surface. That is, one catalyst component 11 is only impregnated in the pores 6, and the other catalyst component 12 is coated on the surface of the carrier 2.

  Thus, even if one catalyst component 11 is only impregnated in the pores 6 and the surface of the carrier 2 is coated with the other catalyst component 12, the mechanical strength of the exhaust gas catalyst 10 for automobiles is increased. Sufficiently secured, sufficient catalyst amount can be secured, catalyst performance can be improved and pressure loss can be reduced, and engine fuel efficiency can be improved. And compared with the case where WC layer 13 is formed thickly, the usage-amount of a noble metal can be reduced and cost can be reduced. In addition, the amount of catalyst coated on the wall surface of the honeycomb cell wall 5 can be reduced, the automobile exhaust gas catalyst 10 can be reduced in weight, and the purification performance can be improved.

  Although the porosity of the carrier 2 is about 50%, it is preferably 30% or more from the viewpoint of WC component impregnation, and more preferably 40% or more and 60% or less from the viewpoint of practical strength.

  Further, the case where the exhaust gas catalysts 1 and 10 for automobiles are DOCs has been described, but the present invention is not limited to this, and the exhaust gas catalysts 1 and 10 for automobiles are DPFs (diesel particulate filters) carrying noble metal catalyst components. It may be a DeNOx catalyst.

DESCRIPTION OF SYMBOLS 1 Exhaust gas catalyst for motor vehicles 2 Support | carrier 3 Catalyst component 6 Pore 10 Exhaust gas catalyst for motor vehicles 11 Catalyst component 12 Catalyst component

Claims (3)

  In an automobile exhaust gas catalyst in which a catalyst component is supported on a ceramic carrier formed in a honeycomb shape, the carrier is formed into a porous body having a plurality of pores, and the catalyst component is impregnated in the pores. An exhaust gas catalyst for automobiles.   The exhaust gas catalyst for automobiles according to claim 1, wherein the porosity of the carrier is 30% or more and 60% or less.   The exhaust gas catalyst for automobiles according to claim 1 or 2, wherein the catalyst component is only impregnated in the pores, and the surface of the carrier is coated with another catalyst component having a composition different from that of the catalyst component. .

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