JP2017170401A - Catalytic converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalytic converter having excellent warming performance and a pressure loss reduction function directly after engine startup.SOLUTION: Provided is a catalytic converter 10 provided with a base material 1 with a honeycomb structure having a barrier 1a with a cell structure through which an exhaust gas circulates, and with a catalyst layer formed on the surface of the barrier 1a. The base material 1, in the cross-section orthogonal to the longitudinal direction as the flowing direction of the exhaust gas of the base material 1, has a central region 2 whose cell density is relatively high and a peripheral region 3 whose cell density is relatively low, and, provided that the thickness of the barrier in the central region 2 is defined as ta and the cell density is defined as Ma, the thickness of the barrier in the peripheral region 3 is defined as tb and the cell density is defined as Mb, ta<tb and 0.8≤ta/tb<1, 1≤Ma/Mb≤1.17, provided that 0.6≤ta/tb<0.8, 1≤Ma/Mb≤1.26, provided that 0.4≤ta/tb<0.6, 1≤Ma/Mb≤1.37, and, provided that 0.2≤ta/tb<0.4, 1≤Ma/Mb≤1.47.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a catalytic converter that is housed and fixed in a pipe constituting an exhaust gas exhaust system.

  Various industries are making various efforts to reduce environmental impact on a global scale. Among them, in the automobile industry, not only gasoline engine cars with excellent fuel efficiency, but also hybrid cars and electric cars. The development of the so-called eco-cars such as the above and the further improvement of its performance is being promoted every day.

  In addition to the development of such eco-cars, research on exhaust gas purification catalysts that purify exhaust gas discharged from engines has been actively conducted. This exhaust gas purification catalyst includes an oxidation catalyst, a three-way catalyst, a NOx occlusion reduction catalyst, etc., and the exhaust gas purification catalyst exhibits the catalytic activity of platinum (Pt), palladium (Pd), rhodium ( Rh) and the like, and the noble metal catalyst is generally used in a state of being supported on a support made of a porous oxide such as alumina.

Generally, a catalytic converter for purifying exhaust gas is disposed in an exhaust gas exhaust system that connects the vehicle engine and the muffler. Engines may emit substances that are harmful to the environment, such as CO, NOx, unburned HC, and VOCs, and precious metal catalysts such as Rh, Pd, and Pt are used to convert these harmful substances into acceptable substances. By passing exhaust gas through a catalytic converter in which the catalyst layer supported on the carrier is disposed on the cell wall surface of the substrate, CO is converted to CO ₂ , NOx is converted to N ₂ and O ₂ , HC and VOC Burns to produce CO ₂ and H ₂ O.

  By the way, the evolution of catalytic converters for improving the fuel efficiency of vehicles has led to a decrease in exhaust gas temperature, and it has become a challenge to reduce emissions immediately after engine start.

  In order to reduce the emissions immediately after starting the engine, measures such as placing the catalytic converter as close to the engine as possible and increasing the thermal energy at the time of charging are required to quickly raise the temperature to the temperature at which the catalyst is activated. Has been tried.

  However, it is difficult to say that the increase in thermal energy is a preferable measure because it causes a deterioration in fuel consumption and reduces the merchantability of the vehicle.

  Here, Patent Document 1 has a plurality of cell density regions configured so that the cell density changes stepwise in the radial direction, and a boundary wall is provided between adjacent cell density regions. A honeycomb structure is disclosed. More specifically, the plurality of cell density regions have the highest cell density except for the outermost cell density region and the highest cell density except for the innermost cell density region. Assuming that the entire honeycomb structure has a low cell density region and has a low cell density region, the actual volume of the honeycomb structure is assumed to be V, the actual volume of the high cell density region of the honeycomb structure is Va, low When the actual volume of the cell density region is Vb, and the actual volume of the boundary wall separating the low cell density region and the cell density region immediately inside it is Vs, the relationship of V−Va ≧ Vb + Vs is satisfied. is there.

JP 2013-173134 A

  According to the honeycomb structure disclosed in Patent Document 1, the thermal shock resistance can be improved while sufficiently ensuring the exhaust gas purification performance. However, there is no regulation that does not cause an increase in pressure loss when defining the relationship between the thicknesses of the partition walls in the central region and the peripheral region and the cell density ratio.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a catalytic converter that does not increase pressure loss.

  In order to achieve the above object, a catalytic converter according to the present invention is a catalytic converter having a honeycomb structure base material having a cell structure partition wall through which exhaust gas flows and having a catalyst layer formed on the surface of the partition wall. The base material has a central region having a relatively high cell density and a peripheral region having a relatively low cell density in a cross section perpendicular to the longitudinal direction that is the flow direction of the exhaust gas of the base material, and the central region When the partition wall thickness is ta and the cell density is Ma, the partition wall thickness in the peripheral region is tb and the cell density is Mb, ta <tb, and 0.8 ≦ ta / tb <1, 1 ≦ Ma /Mb≦1.17, 0.6 ≦ ta / tb <0.8, 1 ≦ Ma / Mb ≦ 1.26, 0.4 ≦ ta / tb <0.6, 1 ≦ Ma / Mb ≦ 1.37, 0.2 ≦ ta When /tb<0.4, 1 ≦ Ma / Mb ≦ 1.47.

  In the catalytic converter of the present invention, the base material is composed of a central region having a relatively high cell density and a peripheral region having a relatively low cell density, and the partition wall thickness in the central region is ta and the cell density is Ma. When the partition wall thickness in the peripheral region is tb and the cell density is Mb, ta <tb, and when 0.8 ≦ ta / tb <1, 1 ≦ Ma / Mb ≦ 1.17 and 0.6 ≦ ta / tb When <0.8, 1 ≦ Ma / Mb ≦ 1.26, when 0.4 ≦ ta / tb <0.6, 1 ≦ Ma / Mb ≦ 1.37, when 0.2 ≦ ta / tb <0.4, 1 ≦ Ma / Mb By defining that ≦ 1.47, it is possible to suppress an increase in pressure loss.

  In other words, even after the engine is started at a low exhaust gas temperature, the heat spot is formed on the honeycomb structure substrate, so that the thickness of the cell structure partition is reduced within a range that does not increase pressure loss, thereby reducing the heat capacity. The temperature of the exhaust gas from the engine can be raised quickly, and the catalyst of the catalytic converter can be activated early (coexistence of excellent warm-up performance immediately after engine startup and pressure loss reduction performance).

  Here, as the base material of the cell structure to be used, in addition to ceramic materials such as cordierite and silicon carbide composed of a composite oxide of magnesium oxide, aluminum oxide and silicon dioxide, other than ceramic materials such as metal materials The thing of a material is mentioned. In addition, a so-called honeycomb structure having a large number of lattice contour cells such as a quadrangle, a hexagon, and an octagon can be applied.

In addition, as a carrier constituting the catalyst layer formed on the cell wall surface of the substrate, at least one of ceria (CeO ₂ ), zirconia (ZrO ₂ ) and alumina (Al ₂ O ₃ ) which are porous oxides is used. Examples of the main component oxide include CeO ₂ , ZrO _2, and Al ₂ O ₃ oxides, and composite oxides of two or more types (so-called CZ material CeO ₂ -ZrO _{2 compounds, Al 2 O 3 -CeO 2 -ZrO} 2 ternary composite oxide Al ₂ O ₃ was introduced as a diffusion barrier (ACZ material), etc.) can be mentioned.

  The catalytic converter of the present invention preferably has a cordierite honeycomb carrier having excellent thermal shock resistance, but may be an electrically heated catalytic converter (EHC). This electric heating type catalytic converter, for example, attaches a pair of electrodes to a honeycomb catalyst and heats the honeycomb catalyst by energizing the electrodes, thereby increasing the activity of the honeycomb catalyst and detoxifying the exhaust gas passing therethrough. In addition to purifying the exhaust gas at normal temperature, the exhaust gas can be purified by activating the catalyst by electric heating when cold, in addition to purifying the exhaust gas at normal temperature, by applying it to an exhaust gas exhaust system that connects the vehicle engine and the muffler.

  As can be understood from the above description, according to the catalytic converter of the present invention, the base material is composed of a central region having a relatively high cell density and a peripheral region having a relatively low cell density, and then a partition wall in the central region. When the thickness of the wall is ta and the cell density is Ma, and the partition wall thickness in the peripheral region is tb and the cell density is Mb, ta <tb, and when 0.8 ≦ ta / tb <1, 1 ≦ Ma / Mb ≦ 1.17, 0.6 ≦ ta / tb <0.8, 1 ≦ Ma / Mb ≦ 1.26, 0.4 ≦ ta / tb <0.6, 1 ≦ Ma / Mb ≦ 1.37, 0.2 ≦ ta / By defining that 1 ≦ Ma / Mb ≦ 1.47 when tb <0.4, the catalytic converter has excellent warm-up performance and pressure loss reduction performance immediately after engine startup.

It is the schematic diagram explaining embodiment of the catalytic converter of this invention. It is a time-vehicle speed graph explaining evaluation of emission. It is the figure which showed the experimental result in the case of 0.8 <= ta / tb <1, Comprising: (a) is the figure which showed the result regarding pressure loss, (b) is the figure which showed the result regarding emission. It is the figure which showed the experimental result in the case of 0.6 <= ta / tb <0.8, Comprising: (a) is the figure which showed the result regarding pressure loss, (b) is the figure which showed the result regarding emission. It is the figure which showed the experimental result in the case of 0.4 <= ta / tb <0.6, Comprising: (a) is the figure which showed the result regarding pressure loss, (b) is the figure which showed the result regarding emission. It is the figure which showed the experimental result in the case of 0.2 <= ta / tb <0.4, Comprising: (a) is the figure which showed the result regarding pressure loss, (b) is the figure which showed the result regarding emission. It is the figure which showed the experimental result in the case of ta / tb> = 1, (a) is the figure which showed the result regarding pressure loss, (b) is the figure which showed the result regarding emission. (A) is the figure which summarized Fig.3 (a)-FIG.7 (a), (b) is the figure which summarized FIG.3 (b)-FIG.7 (b). It is the figure which showed the experimental result which verifies the area ratio of a center area | region and a peripheral area | region, pressure loss, emission, and intensity | strength, (a) is the figure which showed the result regarding pressure loss, (b) shows the result regarding emission. (C) is the figure which showed the result regarding intensity | strength.

  Hereinafter, embodiments of the catalytic converter of the present invention will be described with reference to the drawings.

(Embodiment of catalytic converter)
FIG. 1 is a schematic diagram illustrating an embodiment of a catalytic converter of the present invention. First, an exhaust gas exhaust system in which the catalytic converter of the present invention is interposed will be outlined.

  The exhaust system of exhaust gas (not shown) includes an engine, a catalytic converter 10 shown in FIG. 1, a three-way catalytic converter, a sub muffler, and a main muffler, which are connected to each other by a system pipe, and exhaust gas generated by the engine is exhausted. It has become so. In this exhaust system, when the catalytic converter 10 is an electrically heated catalytic converter (EHC), for example, when the engine is started, the honeycomb catalyst constituting the electrically heated catalytic converter is brought to a predetermined temperature as quickly as possible. The exhaust gas flowing from the engine is purified with this honeycomb catalyst, and the exhaust gas that could not be purified with the electrically heated catalytic converter is purified with a three-way catalyst purification device located downstream of it. become. Next, embodiments of the catalytic converter will be described below.

  A catalytic converter 10 shown in FIG. 1 includes a honeycomb-structured substrate 1 having a cell-structure partition wall 1a through which exhaust gas flows and having a catalyst layer (not shown) formed on the surface of the partition wall 1a.

  The base material 1 has a central region 2 having a relatively high cell density and a peripheral region 3 having a relatively low cell density in a cross section orthogonal to the longitudinal direction, which is the flow direction of the exhaust gas.

  Here, examples of the material for the substrate 1 include materials other than ceramic materials such as cordierite and ceramic materials such as silicon carbide, and metal materials made of a composite oxide of magnesium oxide, aluminum oxide and silicon dioxide.

Further, as a carrier constituting a catalyst layer (not shown) formed on the surface of the cell wall of the substrate 1, porous oxides such as ceria (CeO ₂ ), zirconia (ZrO ₂ ), and alumina (Al ₂ O _{3) are used.} ), An oxide composed of at least one of CeO ₂ , ZrO ₂ and Al ₂ O ₃ , or a composite oxide composed of two or more (so-called CZ materials) CeO ₂ -ZrO ₂ compound _{is, Al 2 O 3 -CeO 2 -ZrO} 2 ternary composite oxide Al ₂ O ₃ was introduced as a diffusion barrier (ACZ material), etc.) can be mentioned.

  The substrate 1 is formed of a honeycomb structure having a large number of lattice contour cells such as a quadrangle, a hexagon, and an octagon.

In the base material 1, the thickness of the partition wall 1a in the central region 2 is ta and the cell density is Ma, the thickness of the partition wall 1a in the peripheral region 3 is tb, and the cell density is Mb.
ta <tb (1)
When 0.8 ≦ ta / tb <1, 1 ≦ Ma / Mb ≦ 1.17
When 0.6 ≦ ta / tb <0.8, 1 ≦ Ma / Mb ≦ 1.26
When 0.4 ≦ ta / tb <0.6, 1 ≦ Ma / Mb ≦ 1.37
When 0.2 ≦ ta / tb <0.4, 1 ≦ Ma / Mb ≦ 1.47 (2)

  As a result of verification by the present inventors described below, it has been proved that the catalytic converter 10 having the above characteristics has excellent warm-up performance and pressure loss reduction performance immediately after engine startup.

(Experiment and results of specifying cell density ratio according to the thickness ratio of the central and peripheral partition walls)
The present inventors manufactured catalytic converters according to Examples (and Reference Examples) and Comparative Examples, and according to the experimental results regarding pressure loss and emissions of the Examples with respect to the Comparative Examples, according to the thickness ratio of the partition wall between the central region and the peripheral region. An experiment was conducted to identify the cell density ratio.

The manufacturing method of the catalytic converter of the comparative example is that the cell shape is a hexagonal cell, the partition wall thickness is 152 μm, the cell density is 600 cpsi (pieces / cm ² ), and the substrate dimensions are 103 mm in outer diameter and 105 mm in length. Yes, the material contains kaolin, fused silica, aluminum hydroxide, alumina, talc, carbon particles, which are raw material powders of cordierite ceramic raw material, the chemical composition ratio is SiO ₂ 45-55% by mass ratio, Al ₂ A ceramic raw material was obtained by adjusting cordierite to be 33 to 42% O _{3 and} 12 to 18% MgO so as to be a main component, adding a predetermined amount of water and binder, and kneading. Next, the ceramic material was extruded using an extrusion mold having hexagonal cell-shaped slit grooves, and the honeycomb formed body was fired at the highest temperature (1390 to 1430 ° C.). After that, a slurry of a three-way catalyst (containing at least one kind of precious metals Pt, Rh, Pd, γ-alumina, and further containing an oxygen storage agent such as ceria) is poured into the base material, and unnecessary parts are blown off with a blower. The material was coated on the wall surface, and moisture was blown for 2 hours with a drier kept at 120 ° C., followed by baking at 500 ° C. for 2 hours in an electric furnace.

  On the other hand, the examples and reference examples were manufactured by the same manufacturing method as the comparative example, but regarding the configuration of the base material, the thickness of the partition walls was different and the cell area had a central region and a peripheral region. It is different from the comparative example. The base material has an outer diameter of 103 mm and a length of 105 mm, and is made of cordierite. Table 1 below shows evaluation levels of Comparative Examples and Examples or Reference Examples 1 to 16. In addition, the test body No. of an Example and a reference example shall be a serial number, and is shown by E1-E16.

Regarding the evaluation method, the pressure loss was evaluated by measuring the pressure loss (25 ° C. equivalent) when air of 6 m ³ / min was passed through each catalytic converter and evaluating the ratio relative to the value of the comparative example.

  For exhaust gas purification performance evaluation, each catalytic converter is installed in the exhaust system of a V-type cylinder 4.3 liter gasoline engine, and the catalyst bed temperature is 1000 ° C for 1 minute, including feedback, fail cut, rich, and lean for 50 hours. An endurance test was conducted, and the amount of emissions (cold performance) emitted during traveling in a predetermined mode was measured. Again, the emission ratio of the example was determined based on the emission amount of the comparative example. FIG. 2 shows a time-vehicle speed graph explaining the evaluation of this emission.

  Furthermore, strength evaluation was evaluated by an isostatic strength test. This strength test is based on the automobile standard (JASO) M505-87 issued by the Japan Society for Automotive Engineers. A pressure vessel with a 20mm thick aluminum plate in contact with both axial end surfaces of the ceramic honeycomb structure substrate constituting the catalytic converter to seal both ends, and the outer wall surface closely adhered with 2mm thick rubber The water was poured into the pressure vessel, hydrostatic pressure was applied from the outer wall surface, and the pressure at the time of destruction was measured to obtain isostatic strength. Again, the isostatic strength ratio of the example was determined based on the isostatic strength of the comparative example.

  3 to 7 show experimental results when 0.8 ≦ ta / tb <1, experimental results when 0.6 ≦ ta / tb <0.8, experimental results when 0.4 ≦ ta / tb <0.6, and 0.2 ≦ ta / t, respectively. It is the figure which showed the experimental result in the case of tb <0.4, and the experimental result in the case of ta / tb> = 1, (a) is the figure which showed the result regarding pressure loss, (b) is the figure regarding emission. It is the figure which showed the result. 8A is a diagram summarizing FIGS. 3A to 7A, and FIG. 8B is a diagram summarizing FIGS. 3B to 7B. Further, FIG. 9 is a diagram showing experimental results for verifying the area ratio of the central region and the peripheral region, pressure loss, emission, and strength, and FIG. 9A is a diagram showing the results regarding pressure loss. (B) is the figure which showed the result regarding an emission, FIG.9 (c) is the figure which showed the result regarding an intensity | strength.

  3-8, when 0.8 ≦ ta / tb <1, the range is 1 ≦ Ma / Mb ≦ 1.17, when 0.6 ≦ ta / tb <0.8, the range is 1 ≦ Ma / Mb ≦ 1.26, and 0.4 ≦ ta / When tb <0.6, the range is 1 ≦ Ma / Mb ≦ 1.37, and when 0.2 ≦ ta / tb <0.4, the range is 1 ≦ Ma / Mb ≦ 1.47. It has been demonstrated that

  Further, FIG. 7 shows that both the pressure loss ratio and the emission ratio deteriorate when ta ≧ tb.

  On the other hand, as shown in FIG. 9, the area ratio between the central region and the peripheral region that satisfies both the pressure loss ratio and the strength ratio (the area Sa of the central region, the area Sb of the peripheral region, Sa / Sb) is in the range of 2 or less. Has been demonstrated.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Center area | region, 3 ... Peripheral area | region, 10 ... Catalytic converter

Claims (1)

A catalytic converter having a honeycomb structure base material having a cell structure partition wall through which exhaust gas flows and having a catalyst layer formed on the surface of the partition wall,
The base material has a central region in which the cell density is relatively high and a peripheral region in which the cell density is relatively low in a cross section orthogonal to the longitudinal direction that is the flow direction of the exhaust gas of the base material,
The partition wall thickness in the central region is ta and the cell density is Ma, the partition wall thickness in the peripheral region is tb and the cell density is Mb,
ta <tb,
When 0.8 ≦ ta / tb <1, 1 ≦ Ma / Mb ≦ 1.17,
When 0.6 ≦ ta / tb <0.8, 1 ≦ Ma / Mb ≦ 1.26,
When 0.4 ≦ ta / tb <0.6, 1 ≦ Ma / Mb ≦ 1.37,
When 0.2 ≦ ta / tb <0.4, 1 ≦ Ma / Mb ≦ 1.47,
Catalytic converter.

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