Patent Publication Number: US-8992821-B2

Title: Pass-through catalytic substrate including porous ceramic beveled corner portions and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims the benefit of priority to U.S. patent application Ser. No. 13/307,818, filed on Nov. 30, 2011, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates generally to apparatus and methods for producing a pass-through catalytic substrate and, more particularly, to apparatus and methods for producing a pass-through catalytic substrate that includes porous ceramic beveled corner portions. 
     BACKGROUND 
     Apparatus and methods are known to produce pass-through catalytic substrates for treating exhaust from gasoline and diesel fueled internal combustion engines. It is known to provide a honeycomb substrate with catalyst coatings within the flow channels of the substrate. In operation, exhaust gas is forced to pass through the flow channels of the substrate. When passing through the flow channels, pollutants like unburned hydrocarbons, carbon monoxide, nitric and nitrous oxides react on catalysts in the washcoatings to form innocuous species like nitrogen, carbon dioxide, and water before the exhaust is released to the atmosphere. 
     During a typical engine start up, a significant amount of time may pass before the pass-through catalytic substrate is heated to a temperatures where the catalyst is active and capable of processing the pollutants. Consequently, a significant amount of pollution escapes immediately after the engine is started and before the substrate reaches the light-off temperature. As such, in order to reduce excess pollution during engine start-up, there is a desire to provide pass-through catalytic substrates to support the catalyst washcoatings that can be quickly heated to reduce the time necessary to reach the light-off temperature. 
     SUMMARY 
     The following presents a simplified summary of the disclosure in order to provide a basic understanding of some example aspects described in the detailed description. 
     In one example aspect, a pass-through catalytic substrate comprises a plurality of porous ceramic substrate walls defining flow channels extending between an inlet end and an outlet end of the catalytic substrate. The pass-through catalytic substrate further includes a plurality of porous ceramic beveled corner portions positioned at intersecting corners of the substrate walls within the flow channels, wherein the porous ceramic beveled corner portions each have a heat capacity less than about 1.38 J/cm 3 /K. The pass-through catalytic substrate also includes a catalytic washcoat layer coating the porous ceramic substrate walls and the porous ceramic beveled corner portions. 
     In another example aspect, a method of making a pass-through catalytic substrate comprises the steps of extruding a ceramic-forming batch material through a die to form a ceramic-forming substrate including a plurality of substrate walls defining flow channels extending between an inlet end and an outlet end of the ceramic-forming substrate, wherein a plurality of beveled corner portions are coextruded with the plurality of substrate walls. The method further includes the step of firing the ceramic-forming substrate into a porous ceramic substrate, wherein the beveled corner portions comprise porous ceramic including a heat capacity less than about 1.38 J/cm 3 /K. The method also includes the step of coating the porous ceramic substrate walls and the porous ceramic beveled corner portions with a catalytic washcoat layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a pass-through catalytic substrate in accordance with aspects of the disclosure; 
         FIG. 2  is a schematic sectional view of the pass-through catalytic substrate along line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an enlarged view of an example beveled corner portion of the pass-through catalytic substrate taken at view  3  of  FIG. 2 ; 
         FIG. 4  is an enlarged view of a second example beveled corner portion of the pass-through catalytic substrate taken at view  3  of  FIG. 2 ; 
         FIG. 5  is a plot of a loading of a washcoat on the pass-through catalytic substrate as a function of a radius of curvature of the beveled corner portion; 
         FIG. 6  is a first plot of a substrate wall thickness at a central portion of a substrate wall as a function of a radius of curvature of the beveled corner portion and a second plot of a washcoat thickness at the central portion of the substrate wall of the pass-through catalytic substrate as a function of the radius of curvature of the beveled corner portion; 
         FIG. 7  illustrates plots of a heat capacity of the beveled corner portion in a pass-through catalytic substrate having a cell density of about 400 flow channels/inch 2  as a function of the radius of curvature of the beveled corner portion at porosities of about 25%, 40%, 50%, and 60%; 
         FIG. 8  illustrates plots of a heat capacity of the beveled corner portion in a pass-through catalytic substrate having a cell density of about 600 flow channels/inch 2  as a function of the radius of curvature of the beveled corner portion at porosities of about 25%, 40%, 50%, and 60%; 
         FIG. 9  illustrates plots of a total heat capacity of the pass-through catalytic substrate as a function of the radius of curvature of the beveled corner portion at porosities of about 25%, 40%, 50%, and 60%; 
         FIG. 10  depicts a method of making a porous pass-through catalytic substrate in accordance with example aspects of the disclosure; 
         FIG. 11  is a schematic view of an extrusion apparatus in accordance with aspects of the disclosure; and 
         FIG. 12  is an enlarged partial schematic sectional view of an example die member taken at view  12  of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments of the claimed invention are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, the claimed invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These example embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the claimed invention to those skilled in the art. 
       FIG. 1  illustrates a perspective schematic view of a pass-through catalytic substrate  102 . The pass-through catalytic substrate  102  is not necessarily drawn to scale and illustrates only one example schematic representation of a pass-through catalytic substrate  102 . The pass-through catalytic substrate  102  includes an inlet end  104  and an outlet end  106  positioned opposite from the inlet end  104 . A plurality of flow channels  108  extend between the inlet end  104  and outlet end  106 . In one example, substantially all of the flow channels  108  are not plugged and therefore provide for an unobstructed pass flow from the inlet end  104  to the outlet end  106  of the pass-through catalytic substrate  102 . 
     As shown in  FIG. 2 , the flow channels  108  can be formed by a plurality of porous ceramic substrate walls  110  extending longitudinally between the inlet end  104  and outlet end  106  of the pass-through catalytic substrate  102 . The porous ceramic substrate walls  110  can include a range of cross-sectional wall thicknesses from about 30 μM to about 150 μm, such as from about 50 μm to about 100 μm. In further examples, the porous ceramic substrate walls  110  can include substantially the same wall thickness through the length of the pass-through catalytic substrate  102  from the inlet end  104  to the outlet end  106 . 
     The flow channels  108  and porous ceramic substrate walls  110  can each extend in a substantially parallel orientation longitudinally between the inlet end  104  and outlet end  106 . An outer surface  112  can surround the flow channels  108  and porous ceramic substrate walls  110 . The outer surface  112  can extend longitudinally between the inlet end  104  and outlet end  106 . As shown, the outer surface  112  can comprise a circular cylindrical shape having a circular cross-sectional profile. In further examples, the outer surface  112  may have an elliptical, polygonal or other shape. For example, although not shown, the outer surface  112  may have a polygonal shape such as triangular, rectangular (e.g., square) or other polygonal shape. Moreover, as shown, the pass-through catalytic substrate  102  can comprise a single monolithic substrate although the substrate may comprise a segmented substrate wherein many substrates are mounted parallel to one another to provide the desired overall cross sectional configuration. Whether a single monolithic or segmented substrate, various geometries may be incorporated in accordance with aspects of the disclosure. For example, the substrates may comprise a rectangular (e.g., square) cross-sectional outer periphery or other polygonal shape having three or more sides. In further examples, the substrates may have an outer cross-sectional periphery that is circular, oval, or other curved shape. 
       FIG. 2  illustrates an example schematic sectional view of the pass-through catalytic substrate  102  along line  2 - 2  of  FIG. 1 . The pass-through catalytic substrate  102  can have a variety of cell densities, such that a larger or smaller number of flow channels  108  can be provided per unit area. For instance, the cell density can be in the range of from about 100 to 1000 channels/inch 2  of pass-through catalytic substrate  102  cross-section. As such, the examples shown in  FIGS. 1 and 2  are not intended to be limiting, as a range of cell densities are envisioned. 
     In further examples, the cell constructions forming the flow channels can have different configurations. For instance, as shown in  FIGS. 3 and 4 , the arrangement of cells shown in  FIG. 2  is a generally rectangular, such as a square, configuration although further examples may have cell structures with a triangular, or other polygonal configuration. Examples of the present disclosure include a plurality of porous ceramic beveled corner portions positioned at intersecting corners of the substrate walls within the flow channels. 
       FIG. 3  is an enlarged view of a portion of  FIG. 2  illustrating just one possible construction of the flow channels  108 . In the illustrated example, porous ceramic beveled corner portions  114  are positioned at intersecting corners of the porous ceramic substrate walls  110  within the flow channels  108 . The porous ceramic beveled corner portion  114  can be defined by projecting a first plane  114   a  from a first wall surface  116   a  of the adjacent porous ceramic substrate wall  110  and a second plane  114   b  projecting from a second wall surface  116   b  of another adjacent porous ceramic substrate wall  110 . The first and second planes  114   a ,  114   b  intersect with one another along an axis  114   c  wherein the corresponding porous ceramic beveled corner portion  114  is defined by the area between the first plane  114   a , the second plane  114   b  and an interior beveled surface  118 . 
       FIG. 4  is another enlarged view of a portion of  FIG. 2  illustrating another one of many possible constructions of flow channels  208  similar to the flow channels  108  discussed above.  FIG. 4  shows example porous ceramic beveled corner portions  214  positioned at intersecting corners of the porous ceramic substrate walls  110  within the flow channels  208 . The illustrated example porous ceramic beveled corner portion  214  can be defined by projecting a first plane  214   a  from the first wall surface  116   a  of the adjacent porous ceramic substrate wall  110  and a second plane  214   b  projecting from the second wall surface  116   b  of another adjacent porous ceramic substrate wall  110 . The first and second planes  214   a ,  214   b  intersect with one another along an axis  214   c  wherein the corresponding porous ceramic beveled corner portion  214  is defined by the area between the first plane  214   a , the second plane  214   b  and an interior beveled surface  218 . 
     For illustration purposes,  FIGS. 3 and 4  shows one porous ceramic beveled corner portion  114 ,  214  of each of four corresponding adjacent flow channels  108 ,  208 . For illustrative purposes, a single porous ceramic beveled corner portion  114 ,  214  is shown associated with each corresponding flow channel  108 ,  208  with the understanding that all four porous ceramic beveled corner portions  114 ,  214  of each corresponding flow channel  108 ,  208  may be substantially identical to one another. Moreover, as shown, the four porous ceramic beveled corner portions  114 ,  214  of each corresponding flow channel  108 ,  208  may be substantially identical to the corresponding four porous ceramic beveled corner portions  114 ,  214  of many, such as substantially all of the porous ceramic beveled corner portions of the remaining corresponding flow channels  108 ,  208 . In further examples, beveled corner portions of some of the flow channels may be mathematically similar to beveled corner portions of other flow channels. For instance, in some examples, the cross sectional area of central flow channels may be greater than the cross sectional area of some of the peripheral flow channels. For instance, in one example, the porous ceramic substrate walls  110  may be relatively thicker at peripheral portions of the substrate when compared to central portions of the substrate to help increase the strength of the substrate in these areas. In such examples, the porous ceramic beveled corner portions may still have cross sectional footprints that are mathematically similar to one another. 
     The porous ceramic beveled corner portions  114 ,  214  can extend partially or completely along the entire length of the pass-through catalytic substrate  102  between the inlet end  104  and the outlet end  106 . In addition, the porous ceramic beveled corner portions  114 ,  214  can be formed integrally with the porous ceramic substrate walls  110 , such that the porous ceramic beveled corner portions  114 ,  214  can be formed from the same material as the porous ceramic substrate walls  110 . 
     The porous ceramic substrate walls  110  and porous ceramic beveled corner portions  114 ,  214  can be formed from a number of different materials, including cordierite. Furthermore, the porous ceramic substrate walls  110  can porous ceramic beveled corner portions  114 ,  214  may be formed by the same material (e.g., cordierite material) that may have substantially the same pore distribution characteristics although further examples may provide the porous ceramic beveled corner portions  114 ,  214  with a different pore distribution than the pore distribution of the porous ceramic substrate walls  110 . 
     In some examples, both the porous ceramic substrate walls  110  and the porous ceramic beveled corner portions  114 ,  214  can include a porosity in a range of from about 50% to about 75%, such as about 55% to about 65%. Furthermore, both the porous ceramic substrate walls  110  and the porous ceramic beveled corner portions  114 ,  214  can include a median pore size in a range of from about 0.5 μm to about 7 μm, such as from about 1 μm to about 5 μm. 
     The interior beveled surfaces  118 ,  218  of the porous ceramic beveled corner portions  114 ,  214  can include a wide range of surface configurations. For instance, as shown in  FIG. 3 , the porous ceramic beveled corner portions  114  can include a rounded, arcuate surface  118  having a concave shape although the arcuate surface  118  may include a convex or irregular surface topography in further examples. In the illustrated example, the arcuate surface  118  can include a radius of curvature (“R”) in a range of from about 40 μm to about 400 μm although the radius of curvature may extend outside of this range in further examples. 
     In one example, arcuate surface  118  of the porous ceramic beveled corner portions  114  of the pass-through catalytic substrate  102  can have a substantially identical radius of curvature in the range of about 40 μm to about 400 μm. In further examples, the radius of curvature can vary from one flow channel to another flow channel. For example, radius of curvature “R” of the arcuate surface  118  could be increasing or decreasing along a radial axis extending towards the outer surface  112 , such that one flow channel has a different radius of curvature than a second, adjacent flow channel. In this example, the radius of curvature of the arcuate surface  118  could be larger or smaller in the flow channels  108  that are closer to the outer surface  112  as compared to flow channels  108  that are closer to a longitudinal center of the pass-through catalytic substrate  102 . 
     Referring now to  FIG. 4 , an enlarged view of a second example of an intersection of the porous ceramic substrate walls  110  is shown. As shown, the interior beveled surface  218  of the porous ceramic beveled corner portion  214  can further include a substantially planar surface  218  extending between intersecting wall surfaces  116   a ,  116   b  of the porous ceramic substrate walls  110 . In this example, the porous ceramic beveled corner portion  214  can define a substantially triangularly shaped structure positioned in a corner of the flow channel  208  in which a hypotenuse forms the planar surface of the interior beveled surface  218 . The planar surface can be substantially linear such that a cross-sectional profile of the planar surface extends in nearly a straight line between the intersecting wall surfaces  116   a ,  116   b  of the porous ceramic substrate walls  110 . 
     In one example, all of the planar surfaces of the interior beveled surface  218  of the porous ceramic beveled corner portions  214  can have substantially identically sized and shaped planar surfaces. In further examples, the size of the planar surfaces could be larger or smaller for different flow channels  208 . Accordingly, the size of the planar surfaces may be increasing or decreasing along a radial axis extending towards the outer surface  112 , such that one flow channel has a larger planar surface than a second, adjacent flow channel. In this example, the size of the planar surfaces could be larger or smaller in the flow channels  208  that are closer to the outer surface  112  as compared to flow channels  208  that are closer to a longitudinal center of the pass-through catalytic substrate  102 . 
     In other examples, the pass-through catalytic substrate  102  could include a combination of porous ceramic beveled corner portions  114 ,  214 . As such, both the arcuate surfaces  118  and the planar surfaces  218  can be provided in the same pass-through catalytic substrate  102 . For instance, one or a plurality of flow channels could include four porous ceramic beveled corner portions  114  having an interior beveled surface  118  as the illustrated arcuate surface while another or a further plurality of flow channels could include four beveled corner portions  218  having the illustrated planar surfaces. In yet another example, each of a plurality of the flow channels within the pass-through catalytic substrate  102  could include a combination of the interior beveled surfaces  118 ,  218  with respective arcuate and planar surfaces. Therefore, it is to be understood that a variety of combinations of the porous ceramic beveled corner portions within a single pass-through catalytic substrate  102  are envisioned. 
     Referring still to  FIGS. 3 and 4 , a catalytic washcoat layer  120  can be provided as a coating on both of the porous ceramic substrate walls  110  and the porous ceramic beveled corner portions  114 ,  214 . The catalytic washcoat layer  120  can define a surface that the exhaust gas contacts as it flows through the pass-through catalytic substrate  102 . Once the catalytic washcoat layer  120  is sufficiently heated to the light-off temperature, the catalyst within the washcoat layer can react with undesirable hydrocarbon and/or nitrogen oxide emissions from exhaust gas before the cleaned gas is released into the atmosphere. 
     The catalytic washcoat layer  120  can extend partially or completely along the entire length of the pass-through catalytic substrate  102  between the inlet end  104  and the outlet end  106 . The catalytic washcoat layer  120  can provide for a relatively high surface area for the deposition of catalytically promoting material and can include a number of different compositions and materials. For instance, in one example, the catalytic washcoat layer  120  can include a composition of about 75% alumina, 21% ceria zirconia, and 3-4% precious metals. However, it is to be understood that the catalytic washcoat layer  120  can include different compositions in further examples. The catalytic washcoat layer  120  can be loaded onto the pass-through catalytic substrate  102  at a number of different washcoat loadings. In just one example, a washcoat loading may comprise about 0.2 g/cm 3  although other loadings of washcoat may be provided in further examples. 
     The porous ceramic substrate walls  110  and porous ceramic beveled corner portions  114 ,  214  of the pass-through catalytic substrate  102  can be used as a support for a variety of materials that can comprise the catalytic washcoat layer  120 . For instance, in one example, the pass-through catalytic substrate  102  can be used to support a catalytic washcoat layer  120  that includes a three-way catalyst material that is used to process exhaust gases from gasoline powered vehicles. In another example, the pass-through catalytic substrate  102  can be used to support a catalytic washcoat layer  120  that includes a diesel oxidation catalyst that can be used in diesel engine after-treatment systems. In yet another example, the pass-through catalytic substrate  102  can be used to support a catalytic washcoat layer  120  that includes a selective catalytic reduction (SCR) catalyst for treatment of nitrogen oxide (NO x ). 
     The pass-through catalytic substrate  102  of the present disclosure can be used to help convert engine emissions into a less toxic substance. Moreover, pass-through catalytic substrates of the present disclosure can allow the pass-through catalytic substrate  102  to heat relatively quickly to a catalytic light-off temperature where the catalyst within the catalytic washcoat layer  120  more effectively converts engine emissions into a less toxic substance. 
     With regard to the present disclosure, it has been found that an increased porosity of the porous ceramic substrate walls  110  and the porous ceramic beveled corner portions  114 ,  214  along with the inclusion of the porous ceramic beveled corner portions  114 ,  214  in corners of the flow channels  108  can produce a number of advantages. The advantages include, but are not limited to, a reduction in total heat capacity of the pass-through catalytic substrate  102  and a reduction in the total amount of washcoat material used in the pass-through catalytic substrate  102 . Increasing porosity and reducing the washcoat loading can both contribute to the reduction in total heat capacity. Reducing the heat capacity allows the pass-through catalytic substrate  102  to be quickly heated, thereby reducing the time necessary to reach the light-off temperature. Moreover, the reduction in washcoat material can reduce material costs while also contributing to a reduction in the total heat capacity of the pass-through catalytic substrate  102 . 
       FIG. 5  a graph of modeled data wherein the Y-axis is a total washcoat loading (g/cm 3 ) and the X-axis is the radius of curvature “R” (μm) of the arcuate surface of the interior beveled surface  118  of the porous ceramic corner portions  114  illustrated in  FIG. 3 . As such,  FIG. 5  shows a total washcoat loading (g/cm 3 ) of the catalytic washcoat layer  120  in the pass-through catalytic substrate  102  as a function of a radius of curvature (μm) of the arcuate surface of the porous ceramic beveled corner portions  114 . The graph of  FIG. 5  is based on modeled data of an example pass-through catalytic substrate  102  having a wall thickness of the porous ceramic substrate walls  110  of about 2.85 mils (72 μm) and a cell density of about 600 flow channels/inch 2 . As shown, as the radius of curvature “R” of the arcuate surface  118  increases, the total washcoat loading in the pass-through catalytic substrate  102  will decrease. The reduction in washcoat loading is due, at least in part, to the porous ceramic beveled corner portions  114  occupying the corners of the flow channels  108 . For instance, referring to  FIG. 3 , the catalytic washcoat layer  120  tends to accumulate at the intersecting corners of the porous ceramic substrate walls  110  within the flow channels  108  such that the thickness “T1” of the catalytic washcoat layer  120  within the intersecting corner is greater than the thickness “T2” of the washcoat layer  120  at an intermediate portion of the porous ceramic substrate walls  110 . 
     The porous ceramic beveled corner portions  114  can therefore displace washcoat material that would normally have accumulated in the corner portions of the flow channels  108  in the absence of the porous ceramic beveled corner portions  114  (i.e., radius of curvature “R” of 0 μm). As such, the washcoat material is displaced from the corners towards the midpoint location of the porous ceramic substrate walls  110 , i.e., the thickness of the region of the porous ceramic substrate walls  110  along the wall surfaces  116   a ,  116   b  as bounded by its intersection with the beveled surfaces  118 ,  218 . 
     According to  FIG. 5 , the washcoat loading on the pass-through catalytic substrate  102  without porous ceramic beveled corner portions  114  (i.e., radius of curvature “R” of 0 μm) is about 0.2 g/cm 3 . However, the washcoat loading drops to about 0.131 g/cm 3  for a radius of curvature of about 200 μm, a reduction in washcoat loading of about 34.5%. As such, providing the pass-through catalytic substrate  102  with porous ceramic beveled corner portions  114  can produce a lower washcoat loading. More specifically, the washcoat loading will progressively decrease in pass-through catalytic substrates  102  having porous ceramic beveled corner portions  114  having a larger radius of curvature. In one example, the washcoat material can account for about 42% of the heat capacity of the entire pass-through catalytic substrate  102  at a porosity of about 25%. Accordingly, this drop in total washcoat loading can reduce the overall heat capacity of the pass-through catalytic substrate  102 , which, in turn, can allow for the effective temperature and light-off to be achieved faster. Still further, a drop in total washcoat loading can provide a significant cost reduction due since the components of the washcoat are typically expensive. 
     Referring now to  FIG. 6 , a graph of modeled data is provided that illustrates two separate plots for an example pass-through catalytic substrate  102  having a cell density of about 600 flow channels/inch 2 , a porosity of about 60%, and a washcoat loading of about 0.2 g/cm 3 . The first plot  122  is presented with a substrate wall thickness (μm) is depicted on a primary Y-axis (left-most Y-axis) as a function of the radius of curvature (μm) of the arcuate surface of the porous ceramic beveled corner portions  114  depicted on the X-axis of the graph. As shown, as the radius of curvature “R” of the arcuate surface (shown in  FIG. 3 ) increases, the cross-sectional thickness of the porous ceramic substrate walls  110  will decrease. In this example, the cross-sectional thickness of the porous ceramic substrate walls  110  is measured at a midpoint location of the porous ceramic substrate wall  110  roughly halfway between opposing corners of the porous ceramic substrate walls  110 . 
     The reduction in the cross-sectional thickness of the porous ceramic substrate walls  110  is due, at least in part, to the presence of the porous ceramic beveled corner portions  114  occupying the corners of the flow channels  108 . As will be described in more detail below, during an extruding process, ceramic-forming batch material that forms the porous ceramic substrate walls  110  can be partially diverted from the porous ceramic substrate walls  110  to fill in the corners of the flow channels  108  and form the porous ceramic beveled corner portions  114 . This results in porous ceramic substrate walls  110  having a thinner cross-sectional thickness at the midpoint. Accordingly, as the radius of curvature of the arcuate surface increases, the porous ceramic beveled corner portions  114  can have a larger cross-sectional area, thus causing the cross-sectional thickness of the porous ceramic substrate walls  110  to decrease with the same amount of material used to extrude the substrate. 
     Referring still to  FIG. 6 , a second plot  124  is depicted on the graph that shows a thickness of the catalytic washcoat layer  120  (μm) on a secondary Y-axis (right-most Y-axis) as a function of the radius of curvature (μm) of the arcuate surface of the porous ceramic beveled corner portions  114  depicted on the X-axis of the graph. Again, the graph is based on an example pass-through catalytic substrate  102  having a cell density of about 600 flow channels/inch 2 , a porosity of about 60%, and a washcoat loading of about 0.2 g/cm 3 . As shown, as the radius of curvature “R” of the arcuate surface (shown in  FIG. 3 ) increases, the washcoat thickness on the porous ceramic substrate walls  110  will also increase. In this example, the cross-sectional thickness of the catalytic washcoat layer  120  is measured at the midpoint location of the porous ceramic substrate wall  110  roughly halfway between opposing corners of the porous ceramic substrate walls  110 . 
     The increase in the cross-sectional thickness of the catalytic washcoat layer  120  at the midpoint location of the porous ceramic substrate wall  110  is due, at least in part, to the presence of the porous ceramic beveled corner portions  114  occupying the corners of the flow channels  108 . The porous ceramic beveled corner portions  114  can displace washcoat material that would have accumulated in the corner portions of the flow channels  108  in the absence of the porous ceramic beveled corner portions  114  (i.e., radius of curvature “R” of 0 μm). As a result, the porous ceramic beveled corner portions  114  induce the washcoat material to be redistributed from the corner portions of the flow channels  108  towards the midpoint location of the porous ceramic substrate wall  110 . The washcoat material can therefore accumulate towards the midpoint location of the porous ceramic substrate wall  110 , thus leading to a corresponding increased cross-sectional thickness of the washcoat layer  120 . Accordingly, as the radius of curvature of the arcuate surface increases, the porous ceramic beveled corner portions  114  can have a larger cross-sectional area, thus causing a larger cross-sectional thickness of the washcoat layer  120  at the midpoint of the porous ceramic substrate wall  110 . For example, in a pass-through catalytic substrate  102  having porous ceramic beveled corner portions  114  with an arcuate surface having a radius of curvature of about 150 μm, the cross-sectional thickness of the catalytic washcoat layer  120  at the midpoint location is about 85% greater as compared to a pass-through catalytic substrate  102  that does not have porous ceramic beveled corner portions  114 . 
     As a result of displacing excess washcoat from the corners, the overall thickness profile of the washcoat layer  120  can be more uniform and therefore less washcoat is needed overall to achieve the desired washcoat layer thickness. In addition or alternatively, more of the washcoat material can be placed away from the corners of the flow channels  108 , such that the washcoat material is more accessible to pollutant gases for improved catalytic conversion during steady-state and light-off. This can be due, at least in part, to the thinner porous ceramic substrate walls  110  at the midpoint location along with the thicker catalytic washcoat layer  120  with an increasing radius of curvature of the porous ceramic beveled corner portions  114 . 
       FIG. 7  shows a graph of modeled data for an example pass-through catalytic substrate  102  having a cell density of about 400 flow channels/inch 2 , wherein the Y-axis comprises the heat capacity of the beveled corner portion (J/cm 3 /K) and the X-axis comprises the radius of curvature “R” of the arcuate surface (μm). The graph depicts the heat capacity of the porous ceramic beveled corner portion  114  without the introduction of the catalytic washcoat layer  120 . The graph of  FIG. 7  is based on an example pass-through catalytic substrate  102  having a wall thickness of the porous ceramic substrate walls  110  of about 2.85 mils (72 μm). Moreover, the graph of  FIG. 7  depicts four separate porosities of the porous ceramic beveled corner portion  114 . The plot  126  represents a porous ceramic beveled corner portion with a porosity of 25%. The plot  128  represents a porous ceramic beveled corner portion with a porosity of 40%. The plot  130  represents a porous ceramic beveled corner portion with a porosity of 50%. The plot  132  represents a porous ceramic beveled corner portion with a porosity of and 60%. 
     As illustrated, as the radius of curvature “R” increases, the heat capacity of each of the porous ceramic beveled corner portions  114  will also increase. However, the heat capacity of the porous ceramic beveled corner portions  114  is lower with an increased porosity. For instance, the heat capacity is highest with a porosity of 25% represented by curve  126 , and is nearly 0.10 J/cm 3 /K in a pass-through catalytic substrate  102  having porous ceramic beveled corner portions  114  with a radius of curvature of about 300 μm. However, the heat capacity progressively decreases with an increased porosity: about 0.08 J/cm 3 /K, about 0.07 J/cm 3 /K, and about 0.05 J/cm 3 /K for 40% porosity, 50% porosity, and 60% porosity, respectively, with a radius of curvature of 300 μm. Accordingly, providing an increased porosity can produce a reduction in the heat capacity of the porous ceramic beveled corner portions  114 . In a further example, the porous ceramic beveled corner portions each include a porosity in a range of from about 50% to about 75% and a heat capacity in a range of from about 0.69 J/cm 3  K to about 1.38 J/cm 3  K. 
       FIG. 8  shows another graph of modeled data for an example pass-through catalytic substrate  102  having a cell density of about 600 flow channels/inch 2 , wherein the Y-axis comprises the heat capacity of the beveled corner portion (J/cm 3 /K) and the X-axis comprises the radius of curvature “R” of the arcuate surface (μm). The graph depicts the heat capacity of the porous ceramic beveled corner portion  114  without the introduction of the catalytic washcoat layer  120 . The graph of  FIG. 8  is based on an example pass-through catalytic substrate  102  having a wall thickness of the porous ceramic substrate walls  110  of about 2.85 mils (72 μm). Moreover, the graph of  FIG. 8  also depicts four separate porosities of the porous ceramic beveled corner portion  114 . The plot  134  represents a porous ceramic beveled corner portion with a porosity of 25%. The plot  136  represents a porous ceramic beveled corner portion with a porosity of 40%. The plot  138  represents a porous ceramic beveled corner portion with a porosity of 50%. The plot  140  represents a porous ceramic beveled corner portion with a porosity of and 60%. 
     Similar to the graph shown in  FIG. 7 , the graph shown in  FIG. 8  also demonstrates that as the radius of curvature “R” of the arcuate surface  118  increases, the heat capacity of each of the porous ceramic beveled corner portions  114  will also increase at a cell density of about 600 channels/inch 2 . However, the heat capacity of the porous ceramic beveled corner portions  114  is likewise lower with an increased porosity. For instance, as shown by plot  134 , the heat capacity is highest with a porosity of 25%, and is nearly 0.15 J/cm 3 /K in the pass-through catalytic substrate  102  having porous ceramic beveled corner portions  114  with a radius of curvature of about 300 μm. However, the heat capacity progressively decreases with an increased porosity: about 0.12 J/cm 3 /K, about 0.10 J/cm 3 /K, and about 0.08 J/cm 3 /K for 40% porosity, 50% porosity, and 60% porosity, respectively, with a radius of curvature of 300 μm. Accordingly, providing an increased porosity can produce a reduction in the heat capacity of the porous ceramic beveled corner portions  114  at cell densities of both 400 channels/inch 2  and 600 channels/inch 2 . In a further example, the porous ceramic beveled corner portions each include a porosity in a range of from about 50% to about 75% and a corresponding heat capacity in a range of from about 0.69 J/cm 3 /K to about 1.38 J/cm 3 /K. 
     Referring now to  FIG. 9 , a graph of modeled data is illustrated depicting a total heat capacity (J/cm 3 /K) of the pass-through catalytic substrate  102  as a function of a radius of curvature (μm) of the arcuate surface of the porous ceramic beveled corner portions  114 . The Y-axis represents the total heat capacity (J/cm 3 /K) of the pass-through catalytic substrate  102  including the catalytic material forming the catalytic washcoat layer  120 . The X-axis represents the radius of curvature (μm) of the arcuate surface of the porous ceramic beveled corner portions  114 . The graph of  FIG. 9  is based on an example pass-through catalytic substrate  102  having a cell density of about 600 flow channels/inch 2 . Furthermore, the graph includes plots based on a number of different porosities of the pass-through catalytic substrate  102 , ranging from 25% to 60%. The plot  142  represents a porous ceramic beveled corner portion with a porosity of 25%. The plot  144  represents a porous ceramic beveled corner portion with a porosity of 40%. The plot  146  represents a porous ceramic beveled corner portion with a porosity of 50%. The plot  148  represents a porous ceramic beveled corner portion with a porosity of and 60%. 
     Referring first to the plot  142  depicting a pass-through catalytic substrate  102  having a porosity of 25%, the pass-through catalytic substrate  102  exhibits only a small decrease in total heat capacity as the radius of curvature of the arcuate surface is increased from 0 μm to 300 μm. In distinction, referring next to the plot  144  depicting a pass-through catalytic substrate  102  having a porosity of 40%, the pass-through catalytic substrate  102  exhibits a noticeable decrease in total heat capacity of the pass-through catalytic substrate  102 . For instance, in a pass-through catalytic substrate  102  without a porous ceramic beveled corner portion  114  (i.e., radius of curvature of 0 μm), the total heat capacity is about 0.42 J/cm 3 /K while the total heat capacity is about 0.38 J/cm 3 /K with a radius of curvature of about 300 μm. Similarly, the total heat capacity will also show a progressively larger decrease with an increasing radius of curvature at porosities of 50% and 60% as respectively represented by plots  146 ,  148 . 
     In one example, by providing a pass-through catalytic substrate  102  with porous ceramic beveled corner portions  114  having a radius of curvature of about 200 μm versus a pass-through catalytic substrate  102  with radius of curvature of 0 (i.e., no porous ceramic beveled corner portions  114 ), the total heat capacity of the pass-through catalytic substrate  102  with the porous ceramic beveled corner portions  114  can decrease from about 0.349 J/cm 3 /K to about 0.316 J/cm 3 /K, an improvement of about 10.2%. Accordingly, as the radius of curvature “R” of the arcuate surface increases, the total heat capacity of the pass-through catalytic substrate  102  will decrease, with the decrease being more significant at higher porosities. This decrease can be attributed, at least in part, to the porous ceramic beveled corner portions  114  occupying the corners of the flow channels  108 . The porous ceramic beveled corner portions  114  can displace washcoat material that would have accumulated in the corner portions of the flow channels  108  in the absence of the porous ceramic beveled corner portions  114 . Since the washcoat material has a higher heat capacity than the porous ceramic beveled corner portions  114 , a replacement of the washcoat material in the corners of the flow channels  108  with the high porosity beveled corner portions can lead to a decrease in total heat capacity. This decrease in total heat capacity can be beneficial because the pass-through catalytic substrate may be able to reach a desired light-off temperature in less time. 
     With reference still to  FIG. 9 , Table 1 (shown below) presents data relating to heat capacities of materials that can be used in one example of the pass-through catalytic substrate  102 . In the example of Table 1, the composition of the catalytic washcoat layer  120  can be about 75% alumina, 21% ceria zirconia, and 3-4% of precious metals. As shown, the heat capacity of the substrate (cordierite in this example) represents about 58% of the heat capacity of the entire pass-through catalytic substrate  102 . However, increasing the porosity of the substrate from 25% to 55% can lower the heat capacity of the entire pass-through catalytic substrate  102  from about 0.479 J/cm 3  K (see 25% porosity plot curve  142  in  FIG. 9 ) to about 0.365 J/cm 3  K, a reduction of about 24%. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Density  
                   
               
               
                   
                   
                   
                   
                 substrate 
                   
               
               
                   
                   
                   
                   
                 600 cells/ 
                   
               
               
                   
                 Material  
                 Heat 
                 Heat 
                 in 2  2.85  
                 Heat  
               
               
                   
                 Density 
                 Capacity 
                 Capacity 
                 mil wall 
                 Capacity 
               
               
                 Material 
                 (g/cm 3 ) 
                 (J/g K) 
                 (J/cm 3  K) 
                 (g/cm 3 ) 
                 (J/cm 3  K) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Cordierite 
                 2.51 
                 1.10 
                 2.76 
                 0.254 
                 0.279 
               
               
                 (substrate) 
                   
                   
                   
                 (25%  
                 (25%  
               
               
                   
                   
                   
                   
                 porosity) 
                 porosity) 
               
               
                 y-alumina 
                 3.96 
                 1.13 
                 4.47 
                 0.2 
                 0.2 
               
               
                 Ceria-Zirconia 
                 5.9 
                 0.6 
                 3.54 
                   
                   
               
               
                 Platinum 
                 21.4 
                 0.13 
                 2.78 
                   
                   
               
               
                 Rhodium 
                 12.4 
                 0.24 
                 3.00 
                   
                   
               
               
                 Palladium 
                 12 
                 0.24 
                 2.88 
               
               
                   
               
            
           
         
       
     
     Turning now to  FIG. 10 , a method  300  of making the pass-through catalytic substrate  102  is shown while  FIGS. 11 and 12  illustrate schematic features of an example apparatus  400  for producing an extruded honeycomb substrate using the method  300 . As shown in  FIG. 10 , the method  300  can include the step  302  of providing a batch of ceramic-forming batch material. For example,  FIG. 11  shows a schematic illustration of a batch  402  of ceramic forming material. The batch material  402  can then be introduced into an input portion  404  of an extruding device  406 . 
     The method  300  can then include step  304  of extruding the ceramic-forming batch material to form a ceramic-forming substrate  304 . For example, as shown in  FIG. 11 , the extruding device  406  is configured to extrude a batch of the ceramic-forming batch material through a die member  408  to form a ceramic-forming substrate of potentially unlimited length. Once the desired length is achieved, a cutter (not shown) can be used to sever the extruded ceramic-forming substrate to provide the substrate with the desired length. 
     As shown, in one example, the extruding device  406  can include a twin-screw extruder including twin screws  410   a ,  410   b  configured to be rotated by respective motors  412   a ,  412   b  to mix and compress the batch of ceramic-forming batch material as it travels along a path  414  toward the die member  408 . The extruding device  406  includes an extrusion axis wherein the ceramic-forming substrate can be extruded from the die member  408  along an extrusion direction substantially parallel to the extrusion axis. 
       FIG. 12  is an enlarged schematic cross sectional view of an example die member  408  taken at view  12  of  FIG. 11  that may be used in accordance with aspects of the disclosure. As shown, the die member  408  includes feed holes  416  configured to feed batch material in direction  418 , along the path  414 , toward a plurality of die pins  420 . The die pins  420  are spaced apart from one another to define slots  422  designed to form the porous ceramic substrate walls  110  of the pass-through catalytic substrate  102  (best seen in  FIG. 2 ) as the ceramic-forming batch material is drawn into the extruded ceramic-forming substrate with the honeycomb cross-section illustrated in  FIG. 2 . 
     The die pins  420  shown in  FIG. 12  can, in one example, have a square shape to define square-shaped flow channels  108  (best seen in  FIG. 2 ) although other die pin configurations (e.g., triangular, hexagonal, octagonal, etc.) can be selected depending on the desired channel configuration. For instance, in one example, the die pins  420  can include beveled, such as substantially rounded corner portions that can produce the porous ceramic beveled corner portions  114 ,  214  discussed above. In one example, the die pins  420  can include a convex radius of curvature in a range of from about 40 μm to about 400 μm. In yet another example, the die pins  420  could include flat chamfered portions to produces the flat interior beveled surface  218  of the porous ceramic beveled corner portion  214 . In further examples, the die pins  420  may have other corner configurations designed to provide the desired interior beveled surface of the porous ceramic beveled corner portions. 
     Turning back to  FIG. 10 , the method  300  can further include the step  306  of firing the ceramic-forming substrate into a porous ceramic substrate  306 . In one example, the step  302  of providing the batch material may provide the batch material with a pore forming material to achieve the desired porosity in the pass-through catalytic substrate  102 . The pore forming material can include a number of different organic materials or compositions, and, in one example, can include starch. The pore forming material can be burned out during the firing step to generate the pores in the porous ceramic substrate. The desired porosity of the pass-through catalytic substrate  102  can be controlled, at least in part, by the amount of pore forming material provided in the ceramic-forming batch material. For instance, the porosity of the pass-through catalytic substrate  102  can be in a range of about 50% to about 75% or, more particularly, in the range of from about 55% to about 65%. Additionally, the pass-through catalytic substrate  102  can be formed with a pore distribution having a median pore size in a range of from about 0.5 μm to about 7 μm or, more particularly, in the range of from about 1 μm to about 5 μm. 
     The method  300  can also include the step  308  of coating the porous ceramic substrate walls  110  and porous ceramic beveled corner portions  114 ,  214  with a catalytic washcoat layer  120  to achieve the pass-through catalytic substrate  102  illustrated in  FIG. 1 . The catalytic washcoat layer  120  can be applied in a number of ways. For instance, in one example, the porous ceramic substrate can be introduced into a slurry comprised of a desired catalyst washcoat. The slurry can contain, for example, precious metals including, but not limited to, alumina, ceria-zirconia, platinum, rhodium, and palladium. In one example, the catalyst washcoat could include about 75% alumina, 21% ceria zirconia, and 3-4% of precious metals. After infiltration of the catalyst washcoat, the porous ceramic substrate can be agitated to remove excess washcoat material. After drying, the pass-through catalytic substrate  102  is provided with the catalytic washcoat layer  120  forming a coating on the porous ceramic substrate walls  110  and the porous ceramic beveled corner portions  114 ,  214 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.