Composite catalytic converter

There is provided a composite catalytic converter for removing pollutant materials from an exhaust gas stream. The converter is composed of an electrically heatable catalytic converter and a conventional ceramic catalytic converter in juxtaposed or embedded axial relationship whereby axial movement in a downstream direction of the electrically heatable catalytic converter core is resisted.

This invention relates, as indicated, to a composite catalytic converter 
for converting gaseous pollutants in an exhaust gas stream to harmless 
and/or environmentally acceptable gaseous ingredients. These catalytic 
converters include an electrically heatable catalytic converter (EHC) and 
a nonelectrically heatable ceramic catalytic converter in reinforcing 
relation and in a common housing. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
The purpose of a catalytic converter is to convert pollutant materials in 
engine or turbine exhaust, e.g., carbon monoxide, unburned hydrocarbons, 
nitrogen oxides, etc., to carbon dioxide, nitrogen and water. Conventional 
catalytic converters utilize a ceramic honeycomb monolith having square 
straight through openings or cells, catalyst coated alumina beads, or a 
corrugated thin metal foil honeycomb monolith having a catalyst carried on 
or supported by the surface. The catalyst is normally a noble metal, e.g., 
platinum, palladium, rhodium or ruthenium, or a mixture of two or more of 
such noble metals. The catalyst catalyzes a chemical reaction, oxidation, 
reduction, or both, whereby the pollutant is converted to a harmless 
by-product which then passes through the exhaust system to the atmosphere. 
However, this conversion is not efficient initially when the exhaust gases 
and converter are relatively cold. To be effective at a high conversion 
rate, the catalyst and the surface of the converter with which the exhaust 
gases come in contact must be at a minimum elevated temperature, e.g., 390 
F. for carbon monoxide, 570 F. for volatile organic compounds (VOC), and 
1000 F. for methane or natural gas. Otherwise, conversion to harmless 
by-products is poor and cold start pollution of the atmosphere is high. 
Once the exhaust system has come to its operating temperature, the 
catalytic converter is optimally effective. Hence, it is necessary to 
contact relatively cold exhaust gases with hot catalyst to effect 
satisfactory conversion at engine start-up. Both compression ignited 
(diesel) and spark ignited engines have this need. 
To achieve heating of the catalyst, there is provided an electrically 
heatable catalytic converter formed of a corrugated thin metal foil 
monolith which is connected to a voltage source, e.g., a 12 volt or 24 
volt automotive battery, and power applied, preferably before and during 
start-up, to elevate and maintain the temperature of the catalyst at at 
least about 650 F. Reference may be had to copending application Ser. No. 
587,219 filed Sep. 24, 1990 the disclosure of which application is 
incorporated herein by reference, for details of an electrically heatable 
catalytic converter core and a power system for effective heating of the 
metal monolith. 
A problem exists with spirally wound or S-wound corrugated thin metal foil 
catalytic converters which the present invention solves. The corrugated 
thin metal monolith core is subject to telescoping in a severe test which 
the devices must pass. Such telescoping can result in destruction of the 
electrically heatable catalytic converter. This test involves oscillating 
(100-200 Hertz and 28 to 60 G) the device in a vertical attitude at high 
temperature (between 700 and 950 C.) with exhaust gas from a running 
internal combustion engine being passed through the device. If the wound 
core device telescopes in the direction of gas flow or breaks up after a 
predetermined time e.g., 5-200 hours, the device is said to fail the test. 
Usually, the device will fail in 5 hours if it is going to fail. 
It is a principal object of the present invention to provide a device which 
will pass the foregoing test, and thereby be reliable in extreme service 
conditions.. 
Reference may be had to U.S. Pat. No. 3,768,982 to Kitzner dated Oct. 30, 
1973. In this patent, heat from a centrally located electric heater is 
transferred by conduction through a monolithic catalyst support to heat 
the catalyst to optimum operating temperature. Reference may also be had 
to U.S. Pat. No. 3,770,389 to Kitzner dated Oct. 30, 1973 which discloses 
a central electrically heated core within a ceramic monolith, heat being 
transmitted by conduction to the catalyst contained in the openings of the 
ceramic monolith. The heating core is formed of metal sheets, one 
corrugated and the other flat, coated with alumina and also bearing a 
catalyst. The metallic core is heated electrically by virtue of its own 
electrical resistance. Heating by conduction takes too long to solve the 
problem of of atmospheric pollution at start-up. Moreover, the thin metal 
cores of the present invention do not require a flat thin metal sheet in 
alternating relation with a corrugated thin metal sheet. A flat thin metal 
sheet adds about 20% to 30% more weight to the device and necessitates a 
longer heat-up time or higher power input. 
Reference may also be had to U.S. Pat. No. 4,711,009 to Cornelison et al 
dated Dec. 8, 1987 for details of a process for the preparation of 
corrugated thin metal foil with a refractory metal oxide coating thereon 
and having a noble metal catalyst deposited on the oxide surface. This 
foil may be accordion folded or spirally wound to form the electrically 
heatable monoliths hereof. This patent is incorporated herein by reference 
thereto. 
Reference may also be had to International PCT publication number WO 
89/10471 filed Nov. 2, 1989 which discloses an electrically conductive 
honeycomb catalyst support unit useful in automobiles. To obtain a 
suitable electrical resistance between 0.03 and 2 ohms, the honeycomb body 
is subdivided electrically, cross-sectionally and or axially, by gaps 
and/or electrically insulating intermediate layers or coatings so that at 
least one electrical current path having the desired resistance is 
obtained. Heating is controlled by a timed relay. Separate catalytic 
converters in the exhaust line, one or more electrically heatable, the 
other conventional, are disclosed. The basic devices shown in this 
application and its companion WO 89/10470 filed Nov. 2, 1989 may be used 
in the present invention. Spiral wound or S-wound cores are subject to the 
same problem of telescoping under the severe test above described. 
In the following description, reference will be made to "ferritic" 
stainless steel. A suitable formulation for this material is described in 
U.S. Pat. No. 4,414,023 dated Nov. 8, 1983 to Aggens et al. A specific 
ferritic stainless steel useful herein contains 20% chromium, 5% aluminum, 
and from 0.002% to 0.05% of at least one rare earth metal selected from 
cerium, lanthanum, neodymium, yttrium, and praseodymium, balance iron and 
steel making impurities. 
In the following description, reference will also be made to fibrous 
ceramic mat or felt. Reference may be had to U.S. Pat. No. 3,795,524 dated 
Mar. 5, 1974 to Bowman for formulations and manufacture of ceramic fibers 
useful herein. One such material is currently commercially available under 
the registered trademark "INTERAM" from 3-M. 
Reference will also be had to certain pending applications, i.e., Ser. No. 
524,284 filed Apr. 16, 1990, and Ser. No. 587,219. These applications are 
commonly owned with the present application, and the disclosures thereof 
are incorporated herein by reference thereto. 
BRIEF STATEMENT OF THE INVENTION 
Briefly stated, the present invention is a composite polycellular catalytic 
converter comprising a housing, a polycellular electrically heatable 
catalytic monolith consisting of corrugated thin stainless steel having a 
refractory metal oxide coating on at least one surface thereof with a 
noble metal catalyst supported thereon in said housing, and a polycellular 
conventional ceramic catalytic monolith in juxtaposed or physically 
abutting coaxial relation with the electrically heatable catalytic 
monolith in said housing, and means for heating the electrically heatable 
catalytic monolith from a voltage source. In a preferred embodiment, the 
electrically heatable catalytic monolith is resting against or embedded in 
the upstream face of the conventional ceramic catalytic monolith. 
Alternatively, the electrically heatable catalytic monolith may be 
disposed between conventional monolith portions at least one of which 
contains a noble metal catalyst disposed in the cells thereof. 
The conventional ceramic catalytic monolith provides several advantages. 
First, retrofitting with current catalytic converters is relatively easy. 
Second, ceramic provides good heat storage and permits the main catalyst 
unit to light-off pollutants more quickly with less energy loss than, for 
example, with a nonelectrically heatable corrugated thin metal monolith. 
Finally, the ceramic monolith seems to protect the catalyst more 
satisfactorily than a metallic, nonelectrically heatable catalytic 
monolith.

DETAILED DESCRIPTION OF THE DRAWINGS 
As indicated above, the present invention is a composite catalytic 
converter especially for use with internal combustion engines, compression 
or spark ignited, and mobile or stationary. The composite catalytic 
converter utilizes a single housing for an EHC and at least one 
conventional catalytic converter. The conventional catalytic converter is 
a ceramic monolith, e.g., Cordierite, or a Barium/Titanate ceramic. Most 
current automobiles, for example, have ceramic monoliths in the catalytic 
converters. The present invention provides among other things, a means for 
retrofitting current ceramic catalytic converter units with an 
electrically heatable catalytic converter (EHC) whereby the efficiency of 
the unit is improved to remove pollutants normally issuing from the 
exhaust pipe during start-up or cold operation when the catalyst is at a 
temperature below that required for optimum conversion of such pollutants. 
Referring now, more particularly to FIG. 1, there is here shown in 
cross-section a fragment of a composite catalytic converter unit 10 in 
accordance with this invention. The composite 10 is composed of a 
conventional polycellular ceramic monoliths 12 of the type in current use 
on automobiles. These monoliths are well known and may be circular or oval 
in cross section. Such monoliths are porous. They are formed by extrusion 
of a refractory composition and thus have straight-through cells usually 
numbering from about 100 to 400 cells per square inch. The cells may be 
circular, square or triangular in cross section and have a noble metal 
catalyst, e.g., platinum, or palladium, or rhodium, or ruthenium or a 
mixture of two or more of such metals, deposited in the pores of the 
ceramic monolith. 
The ceramic core 12 is desirably supported by a wrapping of fibrous ceramic 
insulation 14 in a steel housing 16. Reference may be had to U.S. Pat. No. 
3,795,524 dated Mar. 5, 1974 to Bowman for examples of fibrous ceramic 
insulation formulations. The steel housing 16 is a conventional housing 
for such ceramic monoliths and like that shown in FIG. 7. However, in FIG. 
1, the forward or upstream end of the housing 16 has been carefully cut 
off adjacent the upstream face of the conventional monolith to permit an 
insertion including an electrically heatable catalytic converter unit 18 
such as shown in FIG. 3. To accommodate the electrically heatable unit 18, 
the forward end of the ceramic core 12 is bored out to provide a recess 20 
having a depth equal to the width of the thin metal foil forming the EHC 
18. There is also provided within the recess 20 an inner recess 21 to 
accommodate the projecting ends of the electrically conducting rods or 
pins about which the individual corrugated metal strips are overfolded. If 
a solid rod or tube having a length equal to the axial dimension of the 
EHC and to which the overfolded ends of the strips are tack welded is 
used, the recess 21 is not necessary. The EHC is formed in a manner 
similar to that described in the aforesaid application Ser. No. 587,219, 
with particular reference to FIGS. 2, 2a and 5 of said application. No 
intra core insulation or separate flat thin metal strips are used in the 
EHC cores of the present invention. As described in U.S. Pat. No. 
4,711,009 supra, the thin metal foil strips are first corrugated, 
preferably in a herringbone or chevron pattern and coated on at least one 
side with a washcoat of refractory metal oxide, e.g., gamma alumina 
desirably including a portion of ceria from 1% to 5% up to as much as 30%, 
and fired to set the coating. Thereafter, an aqueous solution of a noble 
metal catalyst is applied to the refractory metal oxide surface or 
surfaces and the catalyzed coated foil strip heated to a temperature 
sufficient to reduce the water soluble catalyst salt to the catalytically 
active metal. Alternatively, the corrugations may be straight through 
although nonnesting such as described in U.S. Pat. No. 4,810,588 dated 
Mar. 7, 1989 to Bullock et al. These fabrication steps are as described in 
the aforesaid U.S. Pat. No. 4,711,009. The coated catalyst bearing strips 
are then folded once over a wire bar and welded thereto as detailed in the 
aforesaid Ser. No. 587,219, and a plurality of such core elements gathered 
at the projecting wire ends, and then tightly wound in a spiral. The pins 
form a central core through which electric power is supplied to the 
catalytic core. As indicated in Ser. No. 587,219, the free ends of the 
overfolded corrugated strips are provided with electrical contact means 
ultimately to be connected to one of the poles of a direct current voltage 
source. The overfolded strips of corrugated metal without any bars, may, 
as above stated, be directly spot welded to a rod or tube core and the 
tube or rod core connected to one side of a voltage source. 
FIG. 2 shows an EHC having no projecting pins and in juxtaposition with the 
upstream face of the conventional ceramic catalytic core. Usually, the EHC 
has a smaller cross-sectional area than the conventional ceramic core, and 
it is therefore, desirable to recess the EHC at least partially into the 
upstream face of the ceramic core because it keeps the pressure drop 
across the face of the gas intercepting surface about the same. When the 
cross-sectional area of the EHC is equal to or about the same as the 
cross-sectional area of the ceramic core, the EHC may be located against 
the upstream face of the ceramic core in the manner shown in FIG. 2. 
The spirally wound core is then retained in a steel band. FIG. 4 shows a 
blank 22 about 0.75" wide which is conveniently formed of stainless steel, 
e.g., ferritic stainless steel. Centrally located on one edge 24 of the 
blank 22 is a projection 26 integral with the band. The width of the 
forward edge 28 of the projection 26 is desirably 0.75" and the projection 
26 extends outwardly about 0.75". The projection is for the later 
installation of the electrical power post as described below. The sides 30 
are at about a 135 degree angle to the edge line 24. As shown in FIG. 5, 
the blank 18 of FIG. 4 is wrapped in a circle having a diameter equal to 
the tightly compressed spiral core. The circle is not initially closed, 
leaving a gap 32 of about 0.12" to allow for compression of the spirally 
wound core after insertion into the band 22. The band 22 is welded to the 
free ends of the spiral core as described in Ser. No. 587,219 to provide 
good electrical communication between the band 22 and the core 18. 
FIG. 3 shows the EHC assembly in side elevation prior to insertion in the 
ceramic core 12. Central post 34 bilaterally projecting from the spirally 
wound core 18 is the point to which the opposite pole of the direct 
current voltage source is attached. 
FIGS. 6 and 7 show an extension piece 36 configured to fit between the 
transition end cap 38, or adapter 38, which enables connection of the 
catalytic converter to the exhaust pipe of the engine and the main body of 
the catalytic converter housing 16. The extension piece 36 has an oval or 
circular configuration depending on the cross-sectional configuration of 
the catalytic converter housing or cannister 16. The extension piece 36 
includes an oval or circular band 40 and a ground bar 42. The ground bar 
42 is desirably formed of nickel or an alloy of nickel. It extends along 
the minor diameter of an oval extension piece or a diameter of a circular 
piece. 
The ground bar 42 extends through the extension piece 36 and is welded at 
the bottom 48 as shown in FIG. 6 and at the top 46. The projection 44 from 
the top is elongated and threated to accept a cable terminal and retaining 
nut, not shown. 
There is provided a hole 50 through the wall of the extension piece 16 to 
enable the insertion of a thermocouple into the corrugated thin metal core 
18. Details for the structure of the thermocouple lead in are shown in 
Ser. No. 587,219. The junction of the thermocouple is placed in a cell in 
the corrugated thin metal monolith and the leads insulated along their 
length and as they pass through the extension piece 36. 
The positive terminal 52 also extends through the extension piece 36 with 
suitable insulation means generally indicated at 51. There is provided a 
metal bushing 54 welded to a collar 56 which is in turn, welded to the 
extension piece 36. The terminal 52 is encased in an insulating sleeve 54 
to isolate the terminal from electrical contact with the inner end 58 of 
the terminal rod 52. The inner end 58 is then welded to the projection 26 
of the clamping band 22 which, as described above, is welded to the free 
ends of the corrugated thin metal overfolded strips forming the 
polycellular core 18. Thus, the positive pole of a direct current voltage 
source is electrically connected to the voltage source. 
The ground, or negative pole of the direct current voltage source, is 
connected to the projecting end 44 of the ground bar 42. The ground bar 42 
is, upon assembly of the extension piece 36 to the downstream end of the 
converter housing 16, then welded to the central bar 34 formed of the of 
the plurality of projecting rods about which the corrugated thin metal 
strips are overfolded and which have been welded together. These 
operations are fully described in Ser. No. 587,219, supra. The positive 
and negative poles may be reversed, if desired. 
After insertion of the EHC 18 into the recess 20 of the ceramic converter 
body 12 along with the extension piece 36, the transition piece 38 (FIG. 
8) is welded to the outer free edge of the extension piece 36 to complete 
the retrofitted composite catalytic converter, and the entire assembly 
reconnected to the exhaust line 60. 
As indicated above, the EHC is polycellular as is the conventional 
catalytic unit. The EHC monolith has a cell density of from 100 to 700 
cells per square inch, preferably 150 to 300 cells per square inch, and 
the conventional catalytic converter unit, which is usually ceramic, has a 
cell density of from 100 to 400 cells per square inch. If the EHC must be 
separated from the ceramic converter unit for any reason, a ceramic block 
having an axial length of about 2 inches and having a cell density of from 
16 to 36 cells per square inch, desirably with a catalyst deposited in the 
cells, may be inserted between the upstream face of the conventional 
catalytic converter unit and the downstream face of the EHC. 
Thus, when from 1500 to 5000 watts of power from a voltage source, such as 
a 12 volt automobile battery, is connected across the terminals 44 and 52, 
power is supplied to the corrugated thin metal core 18, and because of the 
resistance of the thin metal strip portions, is able to effect heating of 
the electrically heatable catalytic converter very rapidly up to 
conversion temperature of at least about 650.degree. F. in from 2-30 
seconds. 
The embodiment shown in FIGS. 1-9 will withstand the severe test conditions 
for at least 5 hours without experiencing telescoping of the EHC core. 
FIG. 9 shows another embodiment of the present invention wherein the EHC is 
coaxially disposed between and in contact with portions of a ceramic 
monolith. There is shown a housing 70 having transition end caps 72 and 74 
welded thereto for accommodating a standard exhaust pipe 60 as in FIG. 8 
and the oval or circular shape of the housing 70. Centrally located within 
the housing is a pair of axially spaced ceramic catalytic monoliths 78 and 
80. These are inserted in the housing using a ceramic mat cushion 82. In 
the case of ceramic monoliths 78 and 80, the mat 82 serves to reduce the 
opportunity for damage to the monolith units 78 and 80 due to vibration. 
The ceramic mat 82 also serves to restrain axial movement of the ceramic 
monoliths 78 and 80 and thus hold the core of the EHC against axial 
movement or telescoping especially in a downstream direction. 
Disposed between and in contact with monolith units 78 and 80 is an 
electrically heatable catalytic converter 84 built up in the same way as 
the electrically heatable catalytic unit 18 shown in FIG. 1 except that 
the band 86 need not have the projecting portion 26 (FIGS. 4,5). The band 
86 encircles the bundle of spirally wound overfolded corrugated thin metal 
strips 88 in the same manner as shown in the aforementioned Ser. No. 
587,219, FIGS. 1, 2, 2a, 3, 4 and 5 thereof. The bundle of steel rods 34 
(FIG. 3 hereof) project from either side of the spirally wound core 18, 
and corresponding recesses 90 and 92 are bored into the confronting faces 
94 and 96 of the monoliths 78 and 80 to accept the projecting ends 98 and 
100 as shown in FIG. 8. The bore 92 in the downstream monolith 80 
communicates with an axial bore 102 to accept a conducting rod 104 which 
is in turn welded at its inner end 108 to radially extending rod 106. The 
distal extremity of the rod 106 may be welded to the housing 70 at the 
point of exit, and threaded as at 110 to accept a support nut and a 
clamping nut (not shown) to hold a cable terminal from the ground pole of 
the voltage source 112 schematically shown. The positive terminal 113 is 
inserted through an insulated feedthrough 114 in any suitable manner (see, 
for example, the insulated feedthrough shown in FIG. 4, items 74, 76 in 
Ser. No. 587,219, supra). The terminal 113 is welded at its inner end 116 
to the band 86 surrounding and holding the bundle 84. The terminal 113 is 
threaded at its distal extremity 118 to accept and retain a cable from the 
voltage source 112. The monoliths 78 and 80 have from 16 to 400 cells per 
square inch, are desirably formed of extruded ceramic, each 1" to 
3"preferably 2" in axial dimension, and catalysed with a noble metal 
catalyst. The upstream portion 78, or brick 78, may be omitted if desired. 
The bricks 78 and 80 are pushed tight against the EHC unit 84. The fit 
between the ceramic mat 82 and the housing 70 is tight to prevent slippage 
downstream and telescoping of the core 84 of the EHC. The ceramic unit 
O.D. may be the same or different from the EHC O.D. A thermocouple 119 is 
provided. The junction 121 is located within the EHC 84 with the leads 
extending through the housing 70 by means of an insulated feed through 123 
and with an instrument plug 125. 
FIG. 10 shows in cross-section another embodiment of the present invention. 
Here the EHC 120 has a diameter less than the diameter of the ceramic 
portions 122 and 124. The upstream portion 122 is provided with a suitable 
bore 126 and recess 128. The downstream portion 124 is provided with a 
suitable bore 130 and a recess 132. The recesses 128 and 132 are provided 
to accommodate the extending portions 134 and 136 of the core bar 138. The 
downstream recess 132 is counter bored with a hole 140 to accept a current 
carrying axial bar 142 which is welded at its downstream extremity 144 to 
a radial current carrying bar 146 which extends through the housing 148. 
The extension through the housing is insulated from the housing 148 by a 
suitable feedthrough generally indicated at 150. Reference may be had to 
FIG. 3 of Ser. No. 587,219 for details of a suitable feedthrough. The 
confronting faces 152 and 154 of the ceramic portions 122 and 124 are 
axially spaced about 0.5" to accommodate one or more radially extending 
current carrying bars 156 and 158. The inner ends of the bars 156 and 158, 
respectively, are welded to a retaining band 160 binding the plurality of 
overfolded corrugated thin metal foil strips forming the core 120 of the 
EHC as previously described. The outer ends of the bars 156 and 158 are 
conveniently welded to a housing 148. One the bars 156 or 158 may be 
extended and threaded at its distal extremity to accommodate a cable 
attachment lug, not shown. 
FIG. 10 also shows a thermocouple leading into the EHC 120 and existing the 
housing 148 through a suitable feed-through 162 for example, as shown in 
FIG. 3. of Ser. No. 587,219. The ceramic blocks 122 and 124 are held in 
place within the housing 148 by a circumferential ceramic mat 164 
compressed in the space between the housing 148 and the ceramic blocks or 
portions 122 and 124. 
The tight juxtaposition of the ceramic block or portion 124 against the 
downstream end of the core 120 prevents the core 120 from telescoping in a 
downstream direction. 
There has thus been provided a means for enhancing the performance of 
spirally wound, or S-wound corrugated thin metal electrically heatable 
catalytic converters by forming a composite catalytic converter, one 
portion being an EHC and the other being a conventional catalytic 
converter. The two portions are arranged in juxtaposition by embedding the 
EHC partially or wholly within the conventional catalytic converter. The 
composite, which can be either a retrofitted device, as in FIGS. 1-8, or 
an OEM device, FIGS. 9 and 10, is adapted to fit in a conventional exhaust 
system and has the durability to withstand rigorous testing by 
manufacturers and thereby prove durable under extreme user conditions. The 
devices of the present invention can be contained in a single can or 
housing located in the exhaust line under the floor of a vehicle or 
adjacent the engine exhaust manifold.