FIELD OF THE INVENTION
[001] The present invention relates to field of automotive and non-automotive exhaust emission systems. The invention more particularly relates to improvements in honeycomb structure of metallic substrate and its method of manufacturing. The invention also relates to catalytically active devices formed from aforesaid honeycomb structure of metallic substrates, employed for the purpose cleaning the engine-out exhaust gases from a variety of gasoline, CNG, diesel engines. Specifically, devices described above has its applications in (1) Three Way Catalysts for gasoline, CNG, LPG, LNG etc. applications (2) Diesel Oxidation catalysts (3) DeNOx catalysts.
BACKGROUND OF THE INVENTION
[002] Emission regulations are becoming stricter and it has now become necessary to improve the performance of catalysts to meet the emission regulations. Many conventional metallic catalyst substrates are made of two thin layers of metallic foils, one flat and one corrugated. These foils are wound together to create a honeycomb structure which is having passages extending along the length of the honeycomb structure to allow flow of a gas

through the honeycomb structure in a longitudinal direction. These passages act like flow channels (called cells), and the walls of channels are coated with catalytically active material which purifies the exhaust gas when the exhaust gas makes contact with the catalytic material. Higher level of purification and lower pressure loss are the two main objectives to be fulfilled by a catalyst substrate. Methods to improve exhaust gas purification are to use higher cell density substrate to increase its geometric surface area. [003] However, with increasing cell density of the substrate results in increasing the pressure loss which effects the engine performance. This increase in pressure loss can be partially reduced by using lower thickness of metal foil. While reducing the foil thickness is limited by the structural integrity of substrate, the mechanical strength and thermal degradation of substrate become major concerns. It has become difficult to improve the performance using only the conventional approach to improving cell shape and density. Therefore focus was placed on the flow velocity distribution of exhaust gas at the entry of the substrate which improves the contact rate. In general, most of the catalytic converters have been installed with a relatively straight exhaust pipe from the exhaust manifold to avoid severe flow misdistribution. It has been reported that catalyst performance can be efficiently improved by making the flow velocity distribution uniform through an improvement in the diffuser and/or deflectors inside the assembly of a catalytic converter. [004] However, addition of appropriate diffuser and deflectors adds to the total pressure drop across the catalytic convertor assembly. Since catalytic

converter improvements are highly subject to spatial restrictions, it is presumed that there are limits to achieving both a high purification level and low pressure loss. The central area of the frontal face of a brick (about 20% to 45% of the total frontal area) still receives 35 to 60% of the emerging flow with higher velocity. This concentrated flow around the centre area reduces the residence time of the gases in the channels which causes a lower conversion efficiency. Moreover, the higher proportion of hot flow of the exhaust gases also becomes the main reason for thermal degradation of a substrate brick. The peripheral area of the substrate brick (about 55 to 80 % of the total area) gets 40% to 65% of flow. This flow mal-distribution is the factor that makes a brick not well utilized, even though a straight pipe and a diffuser are used for better flow distribution.
[005] With the conflicting goals of achieving both a high purification level and low pressure loss, an attempt was made to control the flow velocity distribution by means of a new honeycomb structure (a compound cell structure having a central area with a higher channel density and a peripheral area with a lower channel density) which has a decreasing pressure drop in a radially outward direction. Therefore, the present invention mainly concentrates on the problem of non-uniform flow distribution that arises in uniform cell density substrate, and attempts to improve purification performance and reduce pressure drop in the metallic substrates.
CITATION LIST - Patent Literature

Patent Literature 1: US 2017/0276048 A1 Patent Literature 2: US 2015/0375204 A1
Problems associated with Related art
[006] There are many substrate designs widely used in catalytic converters to purify the exhaust gases. A simple substrate is made up of two layers of flat and corrugated layers rolled together to form a cylindrical honeycomb design. Such a honeycomb structure body is connected to exhaust pipe facing exhaust gases from the internal combustion engine to purify the gases. The flat and corrugated layers act as walls and form cells after rolling together. The channels are formed along the longitudinal direction of substrate or in the direction of exhaust gases passage. One or more layers of a catalytically active materials are coated on to the walls of each channels to make contact with the exhaust gases while passing through the substrate and purify those environmentally harmful gases.
[007] As emission norms becoming stringent year by year, there is a demand for improving the existing systems and further reduce the emissions. High purification requires reducing the cold emissions which contribute to emissions in the initial ~100-200 seconds, just after engine ignition. To reduce the cold emission particularly, substrate body has to be moved as close as possible to engine or substrate design should be light weight for early light off in low temperatures. One of the options, to make light weight design is by reducing foil thickness which can compromise its thermal

stability at high temperature conditions. It is further required to optimize the utilization of catalyst layer(s) used in substrate by reducing the variations in flow velocity.
[008] Patent literature No .1 has disclosed a honeycomb structure body having cylindrical shape divided into inner and outer sides. Inner side region is with a constant cell density. A cell density of the outer side cells varies a radius direction. The outer side cells are formed on the basis of a relational equation ofy = a(x-b)" + c, where x is a distance on the outer side base section measured from a central point on a radial cross section, y indicates the number of the outer side cells per one cm ' at the distance x, a is a negative constant, b is a radius of the inner periphery of the outer side base section, c is the number of the inner side cells per one cm2, and n is a degree.
[009] However, the method presented in the above described patent literature No.1 only applicable to ceramic catalyst substrates but not to metal catalyst substrates in terms of manufacturing constrains with the above said method. Ceramic catalyst substrates are inherently having higher specific heat and suffer from reduced emission performance during start-up phase. Hence, there is a need to have a practically feasible metallic substrate with uniform flow distribution and enhanced emission performance during start-up phase.
[010] Patent literature No. 2 has disclosed a catalytic converter having different cell densities in a cross section of substrate (i.e. cell density of

centre region of substrate is higher than the peripheral region of substrate) with varying catalyst loading between the two centre and peripheral regions. However, this invention does not discuss about the structural modifications in substrate for flow intermixing inside the substrate and also does not discuss about the method of manufacturing for metallic substrates. The proposed invention facilitates intermixing of flow to give better emission performance as well as reduce pressure drop by employing structural modifications in the substrates.
OBJECT OF THE INVENTION
It is an object of the present subject matter to provide to design and manufacture a compound metallic honeycomb substrate for improved exhaust gas purification by 1) providing uniform distribution of flow through the catalyst substrate for better chemical catalyst utilization, 2) allowing intermixing of exhaust gases between channels as well as between different channel density sections of the substrate 3) increasing the pressure drop reduction in radially outward direction by introducing structural modifications in the foils.
It is another object of the present subject matter is to reduce the cost of the catalytic convertor and to address the issue of spatial restrictions in catalytic converter design with improvements in honeycomb substrate. This is proposed by keeping the chemical composition of the catalytically active coating material either same or different in the inner region & in the

peripheral region and by eliminating the use of diffuser and/or deflector used for uniform flow distribution.
It is yet another object of the present subject matter to provide a novel method of manufacturing the proposed compound metallic substrate for exhaust gas purification.
It is yet another object of the present subject matter to provide a novel catalytically active chemical coating on the said compound metallic substrate for exhaust gas purification.
SUMMARY OF THE INVENTION
Accordingly, in one aspect the invention provides a metallic honeycomb structure having an inlet side and an outlet side connected with flow channels for gas flow, the channels being formed by flat and corrugated metal foils rolled together, the honeycomb structure comprising: plurality of regions separated with each other with a metallic partition (2), the plurality of regions comprising: an inner region (1) having a first number of channels per unit area; a peripheral region (4) having a second number of channels per unit area; wherein the first number of channels are greater than the second number of channels per unit area.
[011] In some embodiments, at least one intermediate region (3) having a third number of channels per unit area is provided between the inner region and the peripheral region, the third number of channels being less than the first number of channels and greater than the second number of channels.

[012] In some embodiments, the ratio of channel density of inner to peripheral region being greater than 1 and less than 6; the ratio of channel density of the inner to intermediate region being greater than 1 and less than 4.
[013] In some embodiments, the each of the regions is coated with chemicals comprising of a specific combination of catalytically active materials.
[014] In some embodiment, the catalytically active materials including a variety oxides, nitrates and hydroxides of aluminium, silicon, titanium, cerium, zirconium, calcium, barium and strontium or in any combinations thereof. [015] In some embodiments, the catalytically active materials including composites selected from the oxides of cerium, zirconium, hafnium, neodymium, praseodymium, or any other rare earth element from the lanthanide series of the periodic table, or in any specific combination thereof. [016] In some embodiments, the catalytically active materials comprising noble metal elements from group VIII of the periodic table, including Platinum, Palladium, Rhodium and Ruthenium or in any combination thereof. [017] In some embodiments, the chemical composition of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.
[018] In some embodiments, the density of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.

[019] In some embodiments, the coating thickness of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.
[020] In some embodiments, apertures are provided in the foils and/or metallic partition thereby allowing intermixing of exhaust gases between channels of the inner, intermediate and/or peripheral regions. [021] In another embodiment, the present invention provides a method of manufacturing a metallic honeycomb structure having an inlet side and an outlet side connected with flow channels for gas flow, the method comprising the steps of: a) manufacturing an inner region and inserting it in a metallic partitioning shell having joining filler materials on its inner & outer surfaces; b) reducing diameter of the inner region by resizing the partitioning shell of the inner region; c) holding the inner region between two flat anvils axially; d) overlaying a second set of flat and corrugated foil over each other and one end of this set is spot welded to an outer side of a first partitioning metallic shell of the inner region; e) wrapping the second set of flat and corrugated foil over the first metallic partitioning shell of the inner region and rolling over the metallic partitioning shell multiple times to form a peripheral region; f) inserting an assembly of the inner and peripheral regions in a second metallic shell having joining filler material on its inner surface and resizing the second metallic shell to reduce the diameter; and g) joining layers (6) by thermally processing the entire assembly.

[022] In some embodiments, the method further comprising steps of providing an intermediate region between the inner and peripheral regions by repeating steps a to f.
[023] In some embodiments additional structural elements are provided to join the metallic portioning shell with the outermost metallic shell so as to increase the structural rigidity & durability of entire assembly, & to prevent displacement of honeycomb structure axially. These structural elements can be placed at the inlet or outlet side. These structural elements are placed so as not to cause significant increase in pressure drop.
BRIEF DESCRIPTION OF THE DRAWINGS
[024] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like components throughout the drawings, wherein:
FIGURE 1 & FIGURE 2 illustrate a cross section view of compound metallic substrate which is having multiple regions with different channels/cells densities in accordance with an embodiment of the present subject matter.
FIGURE 3 illustrates pressure drop variation of uniform channel/cell density substrate with variable channel/cell density substrate at different mass flow rates in accordance with an embodiment of the present subject matter.

FIGURE 4 illustrate a chart showing velocity variation along radial direction in accordance with an embodiment of the present subject matter.
FIGURE 5 illustrates a chart showing space velocity comparison in accordance with an embodiment of the present subject matter.
Figure 6 illustrates space velocity comparison of uniform channel/cell density substrate and variable channel/cell density substrate in accordance with an embodiment of the present subject matter.
FIGURE 7 illustrates space velocity comparison of uniform channel/cell density substrate and variable channel/cell density substrate in accordance with an embodiment of the present subject matter.
FIGURE 8 illustrates space velocity comparison of uniform channel/cell density substrate and variable channel/cell density substrate in accordance with an embodiment of the present subject matter.
FIGURE 9 illustrates a schematic diagram of method of manufacturing in accordance with an embodiment of the present subject matter.
FIGURE 10 illustrates a schematic diagram of an embodiment showing structural reinforcements (5) joining the outermost shell with the central & intermediate shell.

FIGURE 11 illustrates % Improvement in emission with variable cell density substrates vis-a-vis corresponding uniform cell density substrates in accordance with an embodiment of the present subject matter.
DETAILED DESCRIPTION OF THE INVENTION
[025] The embodiments of the present subject matter are described in detail with reference to the accompanying drawings. However, the present subject matter is not limited to these embodiments which are only provided to explain more clearly the present subject matter to the ordinarily skilled in the art of the present disclosure. In the accompanying drawings, like reference numerals are used to indicate like components.
[026] Figure 1 shows detail cross sectional view of compound metallic honeycomb structure in accordance with an embodiment of the present invention. The structure comprising an inner region (4), a peripheral region (3), an intermediate region (2) and an outer shell. In an embodiment, the structure comprising only two regions i.e. inner region and peripheral region. The structure can also comprise an optional intermediate region provided between the inner region and peripheral region. Further, structure can also comprise of multiple intermediate regions provided between the inner and peripheral regions. Advantageously, since the structure is made up of metallic material, the structure has a better cold start performance. [027] Figure 1 deals with an example in which the present invention is applied to an exhaust gas catalyst for purifying exhaust gas discharged from an engine. As shown, the metallic honeycomb structure is having multiple

regions with different cell densities. Also, substrate consists of intermediate metallic partitions (2) acting as a transition region between any of the mentioned regions. In an embodiment, the honeycomb metallic substrate consists of flat and corrugated layers of foil shaped in different geometries with improved performance. The metal foil layers can be joined by different joining methods such as welding, laser welding, adhesives, mechanical locking and brazing, and may or may not require filler material. If the manufacturing process specifies the use of a filler material, then it is applied to both sides of the intermediate metallic partitions (2). On the outermost shell, the filler material may be applied only on the inner surface. [028] In an exemplary embodiment, the substrate includes multiple concentric regions being divided radially throughout. The central region having highest number of channels per unit area, the peripheral region having the least number of channels per unit area and the intermediate region having number of channels per area less than the central region and greater than the peripheral region of the substrate. A compound metallic honeycomb structure body is formed of different regions with each of these regions including a flat foil layer and a corrugated foil layer. The flat foil layer and the corrugated foil layer are wound together to create a three dimensional honeycomb structure having passages extending through the length of the honeycomb structure to allow flow of the exhaust gas through the honeycomb structure in the longitudinal direction.

[029] According to some aspects, at least one of the first foil layer and the second foil layer is structured with a pattern of deformations to form corrugated sheet like structure. The pattern of deformations includes at least one of a sinusoidal, a triangular, a trapezoidal, a square and a rectangular wave pattern. And at least one of the first foil layer and the second foil layer includes flow modifying features protruding in perpendicular direction to its surface. According to some aspects, the first foil layer and the second foil layer have a plurality of apertures to reduce the pressure drop and allow mixing of the gas flowing through the passages in the honeycomb structure. [030] In an embodiment, either or all regions can have structural modifications on either or all foils to alter the flow of exhaust gases flowing through the channels. One of the embodiments of the invention is to have flow modifying features called micro-corrugations on either or all foils forming the honeycomb structures. The micro-corrugations are features protruding perpendicular to the surface of the foil. Advantageously, micro corrugations can be on one or both sides of flat and corrugated sheet so that 100 % channels can be covered. The micro corrugations can cover either partial or full area of the foil. The number of micro corrugations per unit area can be appropriately selected
[031] According to some aspects, the central, intermediate and peripheral regions combine to give multiple regions along the radial direction of the catalyst substrate. The range of regions can vary from 2 or more with decreasing channel or cell density in radially outward direction. According to

some aspects, the central, intermediate and peripheral regions are separated with a distinct metallic partition. According to some aspects, the thickness of metallic partition can range from 0.04 mm to 3mm, more particularly between 0.1 mm to 1.5 mm. According to some aspects, the size & shape of apertures, the number of apertures per unit length on either of foils, the number of micro corrugations per unit area are adjusted in each region so as to radially vary & to reduce the pressure drop in the substrate [032] Another embodiment may include in addition an array of apertures on the foils to allow intermixing of exhaust gases between channels of the honeycomb in either of the region. The number of apertures per unit length of foil are adjusted such that it reduces the pressure drop in the substrate. Another embodiment may include apertures in the foils as well as in the metallic partitions, to allow intermixing of exhaust gases between channels of all the regions.
[033] Advantageously, the addition of apertures and micro corrugations allows adjustment of the pressure drop along the channels, as well as improves the emission performance. The reduction in emission performance due to loss of geometric surface area is compensated and further improved due to the intermixing of exhaust flow between different channels and different regions. In an embodiment, this compound structure with different cell density can have range of cell density from 100 to 600 in center region (4) and 100 to 400 in outer peripheral region (3). It can be extended to three or more cell density regions varying radially. Advantageously, with

improvements in flow uniformity, total surface area of substrate can be reduced by 10-30% by this compound structure without compromising performance. So the catalyst layer and the amount of chemical catalyst also reduces significantly.
[034] Fig 2 describes the pressure drop variation of uniform cell density substrate with variable cell density substrate at different mass flow rates. And it compares different diameter of center substrate of variable cell density substrate with uniform cell density substrates. Results show that percentage variation of variable cell density substrate with respect to uniform cell density substrate ranges from minimum 20% to maximum 40% at different mass flow conditions. Proto no. 2985/2 and VIKPIC BS 54 are variable cell density substrates with center substrate diameter of 100 mm and 80 mm. Both these substrates are having cell density of 400 cpsi in center substrate and 200 cpsi in outer substrate. Proto no. 1906001 is a uniform cell density substrate with cell density of 400 cpsi.
[035] Figure 3 shows velocity variation along radial direction in accordance with an embodiment of the present invention. Uniform cell density substrate is of 400 cpsi and 49% of total flow flows through the 36% of frontal area and 51% of total flow flows through the other remaining 64% of frontal area. According to one example, variable cell density substrate is of 400 & 200 cpsi in center and peripheral regions respectively. The diameter of center region is of 100 mm and the corresponding area of center region is 36% of frontal area. The central region receives 42% of total flow and the remaining

peripheral region receives 58% of total flow. According to another example, variable cell density substrate is of 400 & 300 cpsi in center and peripheral regions respectively. The diameter of center region is of 100 mm and the corresponding area of center region is 36% of frontal area. The central region receives 46% of total flow and the remaining peripheral region receives 54% of total flow.
[036] Figure 4 shows another example of the present invention. As shown, uniform cell density substrate is of 400 cpsi and 34% of total flow flows through the 24% of frontal area and 66% of total flow flows through the other remaining 76% of frontal area. According to one example, Variable cell density substrate is of 400 & 200 cpsi in center and peripheral regions respectively. The diameter of center region is of 80 mm and the corresponding area of center region is 24% of frontal area. The central region receives 27% of total flow and the remaining peripheral region receives 73% of total flow. According to another example, Variable cell density substrate is of 400 & 300 cpsi in center and peripheral regions respectively. The diameter of center region is of 80 mm and the corresponding area of center region is 24% of frontal area. The central region receives 30% of total flow and the remaining peripheral region receives 70% of total flow.
[037] Figure 5 shows yet another example of the present invention. As shown, uniform cell density substrate is of 400 cpsi and 57% of total flow flows through the 44% of frontal area and 43% of total flow flows through the

other remaining 56% of frontal area. According to one example, variable cell density substrate is of 400 & 200 cpsi in center and peripheral regions respectively. The diameter of center region is of 110 mm and the corresponding area of center region is 44% of frontal area. The central region receives 49% of total flow and the remaining peripheral region receives 51 % of total flow.
[038] According to another example of invention, uniform cell density substrate is of 400 cpsi and 49% of total flow flows through the 36% of frontal area, 36% of total flow flows through the 46% of intermediate frontal area and 15% of total flow flows through the 18% of peripheral frontal area. According to one example (Fig 6), variable cell density substrate is of 400, 300 & 200 cpsi in center, intermediate and peripheral regions respectively. The diameter of center region is of 100 mm and the corresponding area of center region is 36% of frontal area. The central region receives 45% of total flow, intermediate region receives 36% of total flow and the remaining peripheral region receives 19% of total flow. According to another example, Variable cell density substrate is of 400, 200 & 100 cpsi in center, intermediate and peripheral regions respectively. The diameter of center region is of 100 mm and the corresponding area of center region is 36% of frontal area. The central region receives 40% of total flow, intermediate region receives 38% of total flow and the remaining peripheral region receives 22% of total flow. According to another example, variable cell density substrate is of 600, 300 & 200 cpsi in center, intermediate and peripheral regions respectively. The

diameter of center region is of 100 mm and the corresponding area of center region is 36% of frontal area. The central region receives 35% of total flow, intermediate region receives 46% of total flow and the remaining peripheral region receives 18% of total flow.
[039] Figure 8 describes the % improvement achieved by the use of variable cell density substrates in an exhaust after treatment device, (over the consisting of uniform cell density substrates) as evaluated on a typical Heavy Duty Vehicle (HDV).
[040] In another embodiment the present invention provides a method of manufacturing a metallic honeycomb structure having an inlet side and an outlet side connected with flow channels for gas flow as described above. [041] Figure 7 shows a schematic diagram of a method of manufacturing in accordance with an embodiment of the present invention. The method of manufacturing is as mentioned below:
A) The central region channels are formed initially with a first foil layer and second foil layer wound together to form a honeycomb structure. A joining filler material is applied on the foil to facilitate joining of both the layers without creating obstacles to the flow within the channels.
B) This central region is inserted into a metallic partition which divides the central region from the intermediate region. This metallic partition has joining filler material on the inner and outer surface which binds the central and intermediate region honeycombs with the metallic partition.

C) This sub-assembly of the metallic partition with central honeycomb inside is held between a set of jaws, more particularly a set of flat anvils. The flat anvils are placed in such a way that each anvil face is touching the inlet and outlet face respectively of the sub-assembly without damaging foil face. A second set of a first foil layer and second foil layer are overlaid over each other and one end of this overlaid foils is spot welded to the outer surface of the metallic partition held between anvils. The set of flat anvils is rotated to wind the second set of spot welded foil layers over the metallic partition until the prescribed diameter of intermediate region is achieved.
D) This sub-assembly consisting of the central region honeycomb, the first metallic partition and the intermediate honeycomb is placed into a second metallic partition. This second metallic partition has joining filler material applied on its inner and on its outer surface (not on outer surface if this is the peripheral region). This subassembly of central region honeycomb, first metallic partition, intermediate honeycomb and second metallic partition is placed in a set of dies which apply a circumferential pressure to reduce the diameter of the second metallic partition and form a tight bond.
E) Steps c & d can be repeated for peripheral region if the compound
substrate has 3 distinct regions of different channel densities.
F) The entire subassembly then undergoes thermal process for joining of the
layers with filler materials.
G) Optionally structural reinforcements may be welded/brazed at the outlet or
inlet face to join the outermost shell with central &/or intermediate shell.

H) The structure described in the preceding paragraphs are eventually coated with catalytically active chemicals consisting of oxides of judiciously selected from alumina, silica & titania, or mixtures thereof, rare earth oxides, oxygen storage components and one or more elements from the group VIII of the periodic table. The said coating is designed to reduce the harmful components such as carbon monoxide, a variety of light & heavy hydrocarbons & oxides of nitrogen, emancipating from the engine, due to the combustion process therein, into the exhaust gas assembly of a vehicle. [042] Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined. [043] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

WE CLAIM:
1. A metallic honeycomb structure having an inlet side and an outlet side connected with flow channels for gas flow, the channels being formed by flat and corrugated metal foils rolled together, the honeycomb structure comprising:
plurality of regions separated with each other with a metallic partition, the plurality of regions comprising:
an inner region (1) having a first number of channels per unit area; a peripheral region (4) having a second number of channels per unit area;
wherein the first number of channels are greater than the second number of channels per unit area.
2. The metallic honeycomb structure as claimed in claim 1, wherein at least one intermediate region (3) having a third number of channels per unit area is provided between the inner region (1) and the peripheral region (4), the third number of channels being less than the first number of channels and greater than the second number of channels.
3. The metallic honeycomb structure as claimed in either claim 1 or claim 2, wherein the ratio of channel density of inner to peripheral region being greater than 1 and less than 6; the ratio of channel density of the inner to intermediate region being greater than 1 and less than 4.

4. The metallic honeycomb structure as claimed in either claim 1 or claim 2, wherein the each of the regions is coated with chemicals comprising of a specific combination of catalytically active materials.
5. The metallic honeycomb structure as claimed in claim 4, wherein the catalytically active materials including a variety oxides, nitrates and hydroxides of aluminium, silicon, titanium, cerium, zirconium, calcium, barium and strontium or in any combinations thereof.
6. The metallic honeycomb structure as claimed in claim 4, wherein the catalytically active materials including composites selected from the oxides of cerium, zirconium, hafnium, neodymium, praseodymium, or any other rare earth element from the lanthanide series of the periodic table, or in any specific combination thereof.
7. The metallic honeycomb structure as claimed in claim 4, wherein the catalytically active materials comprising noble metal elements from group VIII of the periodic table, including Platinum, Palladium, Rhodium and Ruthenium or in any combination thereof.
8. The metallic honeycomb structure as claimed in claim 4, wherein the chemical composition of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.
9. The metallic honeycomb structure as claimed in claim 4, wherein the density of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.

10. The metallic honeycomb structure as claimed in claim 4, wherein the coating thickness of the catalytically active coating materials is either same or different, in the inner region and in each of its peripheral regions.
11The metallic honeycomb structure as claimed in claim either claim 1 or claim 2, wherein apertures are provided in the foils and/or metallic partition thereby allowing intermixing of exhaust gases between channels of the inner, intermediate and/or peripheral regions.
12. The metallic honeycomb structure as claimed in either claim 1 or claim 2, wherein micro corrugations are provided on one or both sides of the foil covering either full or partial area of the foil.
13. A method of manufacturing a metallic honeycomb structure having an inlet side and an outlet side connected with flow channels for gas flow, the method comprising the steps of:
a. manufacturing an inner region and inserting it in a metallic shell
having joining filler materials on its inner & outer surfaces;
b. reducing diameter of the inner region by resizing an outer shell
of the inner region;
c. holding the inner region between two flat anvils axially;
d. overlaying a second set of flat and corrugated foil over each
other and one end of this is set spot welded to an outer side of
a first metallic shell of the inner region;

e. wrapping the second set of flat and corrugated foil over the first
metallic shell of the inner region and rolling over the metallic
shell multiple times to form a peripheral region;
f. inserting an assembly of the inner and peripheral regions in a
second metallic shell having joining filler material on its inner
surface and resizing the second metallic shell to reduce the
diameter; and
g. joining layers (6) by thermally processing the entire assembly.
14. The method of manufacturing the metallic honeycomb structure as claimed in claim 13, wherein the method further comprising steps of proving an intermediate region between the inner and peripheral regions by repeating steps a to f.
15. The method of manufacturing as claimed in claim 13, wherein optionally structural reinforcements are welded/brazed at the outlet or inlet face to join the outermost shell with central &/or intermediate shell.