CA1262438A

CA1262438A - Monolithic catalytic convertor mounting arrangement

Info

Publication number: CA1262438A
Application number: CA000506008A
Authority: CA
Inventors: John D. Ten Eyck
Original assignee: Stemcor Corp
Current assignee: Unifrax 1 LLC
Priority date: 1985-04-16
Filing date: 1986-04-07
Publication date: 1989-10-24
Also published as: ES553981A0; AU5561086A; ES8800740A1; KR860007953A; MX168257B; KR930005290B1; AU596966B2; ES557421A0; ZA862847B; JP2518819B2; ES8800395A1; JPS61241413A

Abstract

MONOLITHIC CATALYTIC CONVERTER MOUNTING ARRANGEMENT
ABSTRACT OF THE DISCLOSURE
A device suitable for use as a catalytic converter for purification of the exhaust gases from an internal combustion engine at continuous operating temperatures in excess of 1600°F and up to 2500°F includes a frangible ceramic monolith catalyst element resiliently mounted in a metallic housing. The monolith is wrapped in a thermally insulating layer of ceramic fibers capable of withstanding continuous exposure to temperatures of at least 2000°F. A layer of intumescent material disposed between the housing and the ceramic fiber layer resiliently secures the monolith in the housing. A method of manufacture of such a device is also described.

Description

3 ~

PATENT ~.

MONOLITHIC CATALYTIC CONVERTER MOUNTING ARRANGEMENT

The present invention relates to a device for treatment of exhaust gases from an internal combustlon englne e.g. a catalytic converter.
More specifically the present invention relates to such devices which include as their catalytic member a frangible ceramic monolith including a plurality of flow channels on which catalyst material is deposlted for interaction with said exhaust gases and to an improved mount~ng for such monolith.

~ackqround 0f The Invention Such monoliths may be formed of a brittle f~reproof ceramic materlal such as aluminum oxlde silicon oxide magnesium oxide zlrcon silicate cordierite or silicon carb~de and the llke. These ceram~c mater~als provide a skeleton type of structure wlth a plurality of tiny f~ow channels. Small shockloads are sufficient to crack or crush the monolith. Due to this brittleness problem which exists when using this type of catalytic device In connection w~th motor vehicles in which the ceramic monolith ls located in a hous~ng connected to the exhaust gas system much effort has been expended in developing means for support of the monolith in its housing so that the monolith would be substantially free of shockloads. Representative of these efforts are the following:
U.S. patent 3 798 00~ discloses securement of a monolithic type catalyst element in its housing by a d~fferentlally hardened f~brous linlng. The monollth is supported by a felted layer or sleeve of ceramic fibers which are compressed between the monolith and a shell. After assembly a suitable rlgidizer binder and adhesive liquid containing a high temperature-resistant materlal such as aqueous colloidal silica is applied to the compréssed layer of ceramic fiber material. The treated unit is thereafter dried in a manner so as to cause migration of the s~lica solids to the exposed ends of the sleeve of ceramic fiber.

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U.S. patent 3 876 384 discloses a monolithic catalyst carrier body whlch ~s res~l~ently rr~ounted ~n a reactor casing by surroundlng the monolith with a protectlve ~acket which lncludes h~ghly heat-resistant steel reinforcing means embedded in ceramlc flber and b~nder means wh~ch itself lncludes a flreproof mortar. The rrlonol~th ~s enveloped by a protective jacket coinprising an ~nner layer and outer layer of ceramic or mlneral fibers whlch are embedded ~n a heat-resistant mortar. Steel reinforcing strips are embedded between the ceram~c fiber layers and grip both of the ceramic fiber layers.
U.S. patent 3 891 396 dlscloses an elastic holder for monollthic catalyst bodies. The holder conslsts of a metalllc corrugated tube which simultaneously forms the outer wall of the exhaust conduit. This corrugated tube is provided with a mechanical bias wh~ch safely holds the monolithic catalyst body and presses it against an end bearing. The monolithic body may be surrounded at its outer surface with elastlc heat-resistant material in the form of ceramic wadding d~sposed in the space between the corrugated tube and the catalyst body or its ceramic sleeve. The c~atalyst body may be cemented with a heat reslstant cement to a ceramic sleeve which serves to thermally lnsulate the corrugated tube from hot exhaust gases.
U.S. patent 3 916 057 discloses a process for mounting monolithic catalyst support elements which utilizes an intumescent sheet material containing vermiculite or other expandable mica. The intumescent sheet materlal functions as a resilient mounting material by expansion in situ. The thermal stability and resilience of the sheet after exfoliation compensate for the difference in thermal expansion of the metal canister and the monolith and absorbs mechanical vibrations transmitted to the fragile monolith or forces whlch would otherwise be imposed on the monolith due to irregular~ties in the metall~c or ceramic surfaces.
U.S. patent q 048 363 dlscloses an offset laminated intumescent mounting mat for use in wrapping a ceramlc catalytlc monolith. After heating expansion of the intumescent materlal ln the mat secures the monolith in its housing or covering.
U.S. patent 4 142 864 discloses mountlng of a catalytlc ceram~c monol~th by posit~on~ng a res~llent flex~ble ceramic flber mat or blanket in the space between the catalytic monol~th and the inner surface of the casing. This blanket is compressed upon installat~on of annular plug members which are inserted at each end of the ceramic monolith between it and the casing. The plugs may be formed of solid metal wire mesh or hollow metal.
U.S. patents 4 2~9 733 and 4 256 700 disclose a catalyst coated ceramic monolith supported in a sheet metal housing by both a wlre mesh sleeve and an intumescent sleeve which are positioned ad~acent each other in non-overlapping fash~on.
U.S. patent 4 269 807 discloses a resilient mounting for a ceramic catalytic monolith in which the monolith is surrounded with a blanket of knitted wire mesh which is partially compressed throughout its length.
Overlying the knitted wlre mesh ls a band of high-temperature ~ntumescent material containing ceramic f~bers as a viscous caulking or-paste withln the matr~x of the metal mesh. Among the constructions disclosed is one whlch includes mach~ning the ceramlc monol~th to remove 1/8 inch from its diameter and coating it with ceramic fibers of the corresponding thickness followed by surrounding w~th a blanket of knitted wire mesh.
U.S. patent 4 305 992 d~scloses flexible ~ntumescent sheet materlals suitable for use in mounting autmotive catalytic converter monoliths.
Tnese materials contain unexpanded ammonium ion-exchanged vermicul~te flakes.
U.S. patent 4 328 187 discloses an elastic holder for axial suspension of a ceramic catalytic monolith within a housing. The monolith is surrounded with a layer of heat-resistant mineral fiber material. Overlying this fiber layer is a jacket or sleeve of good heat-insulating mineral materlal. Overlylng the sleeve is a layer made from a hlghly-elastic material such as foam asbestos or glass fiber f1eece or from a metallic wire mesh cush~on wh~ch serves as a damping elemént which extends w~thin the housing over the entlre length of the monolith and elastically suspends the monoli~h together wlth its ceram~c flber wrapping and sleeve against the walls of the houslng.
U.S. patent 4 335 077 dlscloses support of a ceram~c catalyt~c monolith by means of elast~cally deformable damping r~ngs or envelopes.
In one embodlment the monolith ls surrounded by a protectlve ~acket of heat-resistant cement or putty re~nforced with ceramic f~bers. This protective jacket may be relnforced with metal in the form of a wire mesh or the l~ke. The protective jacket ~s enveloped around its circumference by a soft mineral fiber layer which ls compressed between the housing wall and the protective ~acket.
U.S. patent 4 353 872 discloses support of a ceram~c catalyt~c monolith within its casing by means of a gas seal member formed of heat-resistant and expandable sheet material for example vermiculite quartz or asbestos wh~ch envelopes a portion of the monolith.
Longitudinally displaced therefrom is a separate layer of generally cyllndrically knltted wire or resil~ent support wh~ch is disposed between the monolith and ~ts casing to dampen external forces applied to the monol~th.
U.S. patent 4 425 304 discloses a catalytic converter in which ceram~c catalytic monoliths are supported by an elastic pad of expanded metal or steel mesh fabrics or a knitted web of ceramic fibers at their ends and are wrapped with respective cushioning layers of expanded metal or any other known flame-retardant corrosion-resistant cushioning mater~al.
U.S. patent 4 432 943 di closes an elastic suspension for a monol~thic catalyst body in wh~ch the annular space between the housing and the catalyst body ~s fllled w~th heat-res~stant m~neral fiber material which serves to prevent bypass of exhaust gas and as thermal insulation. In another construction the monolith ls surrounded by a mineral fiber layer and a rigid sleeve of heat-reslstant metal ~s ~2~

positioned over the mineral fiber layer. The annular space between the sleeve and the housing may be filled with ceram~c fiber.
Many of the aforedescribed means for support of a ceramic catalytlc monol~th have been adopted commercially for use in connection with gasol~ne powered passenger automobiles. In thls type of serv~ce the maxlmum converter temperatures are generally under 1600F. When attempts have been made to secure the ceram~c monolith ut~lizing materlals such as those disclosed in U.S. patent 3 916 056 and 4 305 992 ln vehicles having a higher gross vehlcle welght ~GVW) failures have occurred which are bel~eved due to failure of known intumescent sheet materials. One mode of failure observed is fragmentation of the ceramic monolith another mode of failure has been shreddlng of the lntumescent sheet material and consequent plugg~ng of the next monolith in sequence. Large passenger automobiles may utilize catalytlc converters wh~ch ~nclude t~o ceramic monol~ths. Vehicles of higher gross vehicle weight e.g. trucks may require four serially arranged monollths. Because of their high GVW the englnes of such vehicles operate at a much higher percentage of their max~umum outputi a much greater percentage of the~r operating tlme than do the engines in passenger automoblles. These operatin~ conditions in heavier vehicles result in maximum catalytic converter temperatures of much greater than 1600F. Converter monol~th temperatures of 2000F are not uncommon and temperatures of 2500F may be encountered.
A typical passenger automobile catalytic converter utilizes a ceramic monolith which is supported by intumescent sheet material like that described in U.S. patents 3 916 057 or 4 305 992 having a nominal thickness of 0.195 inch and a nominal density of 40 pcf. This material is compressed during installation of the ceramic monolith into its metallic shell to a nominal thickness of 0.130 ~nch and a nominal denslty of about 60 pounds per cubic foot (pcf). Such a construction does not withstand the higher operating temperatures often encounte~ed in the operating cycle of a higher GV~ vehicle such as a truck. To overcome these deficiencies it has been suggested that the overall nominal thickness of the compressed ~nstalled Intumescent layer be increased to about 0.24 inch and the nominal density be increased to about 65-70 pounds per cubic foot as installed. hihile this latter construction does not immediately fail it has been found after operation for a period of t~me that the layer of intumescent sheet mater~al ad~acent the catalyt~c converter was totally degraded thus g~ving rlse to the possibillty of such degraded layer shredding and plugging the next monolith in sequence or the degradatlon continu~ng until the pre-compression force is released and the monolith is free to bounce about within the shell and self-destruct due to mechanical shock.

Brief Summarv Of The Invention The primary purpose of this lnvention is to provide an improved mounting for a frangible ceramic catalytic monolith which is suitable and very convenient for mass manufacture and for use in the exhaust systems of automotive internal combusion engines particularly where converter operating temperatures of 2000F or more are anticipated.
According to the present-~nvention thls purpose is accompl~shed by provislon of a devlce for treatment of exhaust gases from an internal combustion engine comprising:
a~ a housing having an inlet at one end and an outlet at its opposite end through which exhaust gases flow;
b) a frangible ceramic monol~th resiliently mounted within said housing said monolith having an outer surface and an inlet end face at one end in communicat~on with said inlet of said housing and an outlet end face at ~ts opposite end in communicatlon with said outlet of said housing;
c) a ceramlc fiber layer in contact with and cover~ng at least a portion of said outer surface of said monolith; and d) an intumescent layer disposed between said housing and said ceramic fiber layer.

Accordlng to another dspect of the present invent~on there is provided a catalytic converter for purifying exhaust gases of an internal combustion engine comprlsing:
a~ a hollow metallic housing having an inner surface and inlet at one end and an outlet at the other end;
b) a frangible gas-pervious ceramic monolith catalyst element resiliently mounted within sa~d housing said catalyst element having an inlet end face in communication with sald inlet of sald housing and an outlet end face in communication with said outlet end of said housing;
c) means thermally insulating and resiliently mounting said catalyst element in spaced relationship from said houslng comprising;
d) a layer of ceramic fibers capable of resisting continuous exposure to temperatures of at least 2000F covering and in contact with at least 70 percent of said outer surface of said catalyst element between its end faces; and at least one layer of intumescent sheet material covering said ceramic fiber layer and contacting said housing.

Description of the Drawing Figure 1 is a fragmentary isometric view of a device embodying the invention.

Detailed Descriptlon Of The Invention Referring to the Figure there is shown at numeral 10 a catalytic converter generally. Catalytic converter 10 includes a generally tubular housing 12 formed of two pieces of metal e.g. high temperature-resistant steel. Housing 12 includes an inlet 14 at one end and an outlet 15 (not shown) at its opposite end. The inlet 14 and outlet 15 are suitably formed at their outer ends whereby they may be secured to conduits in the exhaust system of an internal combustlon engine. Device 10 contalns a - ` -

3 ~

~4-P-1463 frangible ceramic monolith 18 whlch i5 supported and restrained within hous~ng 12 by layers 20, 22 and 23 to be further descri~d. Monolith 18 lnclude5 a plural~ty of gas-pervious passages wh~ch extend axially from its ~nlet end face at one end to lts outlet end face at its opposlte end. Monollth 18 is constructed of a suitable refractory or ceramic materlal ln known manner and configuration. Monollths are typically oval or round in cross-sectional configuration.
In accordance with the present lnventlon the monolith is spaced from its housing at least about 0.Z inch. The outer surface or monolith 18 is wrapped w~th a layer 20 of ceramic fibers. Preferably for intended monol~th operating temperatures of up to 2000F the ceramic fiber layer 20 has an ~nstalled nominal thickness of at least 0.03 inch and an installed nom~nal density of at least about 40 pcf. Overlying this layer 20 of ceramlc fibers there is provlded a layer 22 23 of intumescent sheet material wh~ch is in contact with the ceramic f~ber layer 20 and the metal hous~ng 12. Preferably the intumescent layer 22 23 has an installed (compressed) nominal thickness of at least about 0.2 inches and an installed nominal density of about 70 pcf.
Preferably and conven~ently layer 20 ls in the form of ceramic fiber paper. However other ceramic fiber forms such as blanket mat or felt may be employed provided they ~mpart the necessary thermal insulation and mechanical support as provided by a layer of ceramic fiber paper.
While in Figure 1 the intumescent material is shown to be provided ln the form of layers 22 and 23 which are superposed upon ceramic fiber layer 20 a single layer of intumescent material may be employed if available in the requisite thickness and denslty. The ceramic fiber paper may be laminated to the intumescent layer prior to assembly in a catalytic device.
Ceramic fiber papers suitable for use in the present invention are preferably free of vermicullte. Small amounts of vermiculite may be present in the ceramic fiber paper layer e.g. up to about 30 weight percent; however the presence of such vermiculite is not recommended and ~ ~2~3~ `3~

may reduce the service temperature and life of monolithlc catalytlc converters employlng such ceramic flber paper. The presence of vermlcullte including ammonlum-ion exchanged types may reduce the effectiveness of the ceramic fiber layer particularly by causing lts degradatlon at temperatures lower than that of the ceramlc fibers in the absence of vermiculite.
An eminently sultable materlal for monolith temperatures up to 2300F
for ceramic fiber layer 20 has been found to be Fiberfra ~ 970 paper available from Sohio Engineered Mater~als Company Nlagara Falls New York. This product ls made from bulk alumino-silicate glassy flber having approximately 50-50 alumina/silica and a 70/30 fiber/shot ratlo.
About 93 weight percent of this paper product is ceramic fiber/shot the remairing 7 percent being in the form of an organic latex binder. For even higher monolith temperatures papers produced from Flbermaxtm polycrystalline mullite ceramic flbers available from thls manufacturer may be employed. Alumina fibers may also be employed where high monolith temperatures are expected.
In a typical assembly intended for use wlth 2-10 -ton trucks the ceramic monolith is of round cross-sectional configuration and measures approximately 6 inches in diameter and has a length of about 3 inche .
For the constructlon of a converter whose monol~th is expected to operate at temperatures up to 2500F a layer of Fibermaxtm ceramic fiber paper having a nominal uncompressed thickness of about 0.125 inch and a nom~nal uncompressed density of about 12 pcf is wrapped around each monolith.
Thereafter two layers of intumescent sheet material like that described in U.S. patents 3 916 057 or 4 305 992 each having a nominal uncompressed thickness of about 0.200 inch and a nominal uncompressed density of 40 pcf are wrapped around the layer of ceramlc fiber paper.
This combination of monolith ceramlc fiber paper and intumescent sheet material layers is then inserted into one of the members corresponding to those wh~ch form housing 12. Thereafter the assembly is lnstalled by radially compresslng between the members of the housing so that the J

comblned thickness of the cer~mic flber paper and intumescent sheet material layers is reduced to about 1/4 inch and the density of the comblned layers is increased to about 70 pounds per cublc foot.
Preferably the ceramic fiber layer and intumescent layers extend longltudinally at least about 70 percent of the monolith length.
Preferably the ceramlc fiber and intumescent layers do not e~tend beyond the length of the monolith. The metal housing extends beyond the ends of the mcnolith. After compres ion of the members forming the housing their edges are elther folded over as illustrated in Figure 1 or welded longitudinally to form a gas-tlght housing.
While not completely understood there appears to be a direct relatlonship between the density of the ceramic fiber paper layer and ~ntumescent material layers and the maxlmum use temperature Or the catalytic device. For example ~hen the maximum lntended monolith service temperature is about 1600F adequate service life is provided when vermiculite-containing intumescent material according to U.S.
patents 3 916 056 and 4 305 992 ~s alone employed at an lnstalled density of about 45-60 pcf. When the maximum intended monolith serv~ce temperature is elevated to 1825F adequate service life rnay be obtained if the installed density of such intumescent material layers is about 70 pcf.
When the maximum lntended service temperature of the monolith is elevated to 2000F such intumescent sheet material even at an installed density of 70 pcf and an installed thickness of Q.240 degrades ad~acent the rr~onolith. Laboratory experiments indicate that provision of a 0.035-inch installed thickness and 43 pcf installed density ceramic fiber paper layer reduces the temperature at interface of the ceramic fiber paper and such intumescent sheet material by 107-114F. Preferably the ceramic fiber paper layer is of sufficient thickness to limit the maximum temperature o~ the lntumescent layer to less than 1900F and ~ore desirably to 1850F or less.

Increasing or decreasing the installed density of the ceramic fiber and intumescent material layers does no~
significantly change th~ thermal insulation properties of these layers per unit of thickness, but does significantly affect the restraining forcQ imposed on the monolith. The restraining force at 75F increases directly with an increase in installed density.

While a presently preferred embodiment of the invention has been illustrated and described, it will be apparent to those skilled in the art that modifications thereof are within the spirit and scope of the invention. For example, the monolith may be an electrically resistant-heated element. The monolith may serve as a regenerable particulate trap. For example, in assemblies where even higher monolith operating temperatures are anticipated, e.g. 2500F, the ceramic fiber paper layer which is in contact with the monolith should be formed, for example, of Fibermaxtm polycrystalline mullite fibers or of alumina fibers to thermally insulate the radially outer layers of vermiculite-containing intumescent material from exceeding their maximum continuous use temperature. The ceramic monolith may be first wrapped in polycrystalline alumino-silicate fiber, then wrapped with vitreous alumino-silicate fiber and then wrapped with intumescent material. The outside temperature of the housing of the catalytic converter may be reduced by increasing the thickness of the combined ceramic fiber and intumescent material layers.
For simplicity of illustration, housing 12 has been shown to be smooth. In most applications, however, it is recommended that the housing be ribbed or otherwise reinforced to stiffen it to resist the force exerted by the compressed ceramic fiber paper and intumescent sheet materials.

"Ceramic fibers" as used herein include those formed from basalt, industrial smelting slags, alumina, alumino-silicates and chrome, zircon and calcium modified alumino-silicates and the like.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Device for treatment of exhaust gases from an internal combustion engine comprising:
a) a housing having an inlet at one end and an outlet at its opposite end through which exhaust gases flow;
b) a frangible ceramic monolith resiliently mounted within said housing said monolith having an outer surface and an inlet end face at one end in communication with said inlet of said housing and an outlet end face at its opposite end in communication with said outlet of said housing;
c) a ceramic fiber layer in contact with and covering at least a portion of said outer surface of said monolith; and d) an intumescent layer disposed between said housing and said ceramic fiber layer.

2. The device of claim 1 wherein said ceramic fiber layer is selected from the group consisting of ceramic fiber mat ceramic fiber blanket ceramic fiber felt or ceramic fiber paper.

3. The device of claim 1 in which said ceramic fiber layer is ceramic fiber paper which contains less than 30 percent by weight of vermiculite. which paper is capable of resisting continuous exposure to temperatures of at least 2000°F.

4. The device of claim 1 in which said ceramic fiber layer is vermiculite-free ceramic fiber paper.

5. The device of claim 3 in which the ceramic fiber paper is of a thickness sufficient to limit the maximum temperature of the intumescent layer to less than. about 1900°F when the monolith is at a continuous operating temperature not exceeding 2500°F.

6. The device of claim 1 in which said ceramic fiber layer is of a thickness sufficient to limit the maximum temperature of the interface between the intumescent layer and the ceramic fiber layer to less than 1850°F when the monolith is at a continuous operating temperature not exceeding 2500 F.

7. The device according to claim 3 wherein the ceramic fiber paper has an installed nominal thickness of at least 0.035 inches and an installed nominal density of at least 40 pounds per cubic feet.

8. The device of claim 4 wherein the intumescent layer contains ion-exchanged vermiculite and the ceramic fiber layer limits the maximum temperature of the intumescent layer to not more than 1850°F during continuous treatment of exhaust gases.

9. The device of claim 8 wherein the monolith is suitable for an operating temperature of greater than 1900°F.

10. The device of claim 8 wherein the monolith is suitable for an operating temperature of at least 1950 F.

11. A catalytic converter for purifying exhaust gases of an internal combustion engine comprising:
a) a hollow metallic housing having an inner surface and inlet at one end and an outlet at the other end;
b) a frangible gas-pervious ceramic monolith catalyst element resiliently mounted within said housing said catalyst element having an inlet end face in communication with said inlet of said housing and an outlet end face in communication with said outlet end of said housing;
c) means thermally insulating and resiliently mounting said catalyst element in spaced relationship from said housing comprising;
d) a layer of ceramic fibers capable of resisting continuous exposure to temperatures of at least 2000°F covering and in contact with at least 70 percent of said outer surface of said catalyst element between its end faces; and e) at least one layer of intumescent sheet material covering said ceramic fiber layer and contacting said housing.

12. The catalytic converter of claim 11 wherein said layer of ceramic fibers is selected from the group consisting of ceramic fiber mat ceramic fiber blanket, ceramic fiber felt or ceramic fiber paper.

13. The catalytic converter of claim 11 wherein said inner layer of ceramic fibers has an uncompressed nominal thickness of at least 1/16 Inch and an uncompressed nominal density of at least 12 pcf.

14. The catalytic converter of claim 11 wherein the ceramic fiber layer has an installed nominal thickness of at least 0.030 inch and an installed nominal density of at least 40 pounds per cubic foot.

15. The catalytic converter of claim 14 wherein said catalyst monolith element is spaced from said housing at least about 0.2 inch.

16. The catalytic converter of claim 14 wherein said intumescent sheet material has an uncompressed nominal thickness of about 0.4 inches an uncompressed nominal density of about 40 pcf and the installed ceramic fiber layer and intumescent sheet material layers have a combined thickness of about 1/4 inch and a combined density of about 70 pcf.

17. The catalytic converter of claim 13 wherein said intumescent sheet material layer has an uncompressed nominal density of about 40 pcf.

18. The catalytic converter of claim 17, including two layers of intumescent sheet material each having an uncompressed nominal thickness of about 0.2 inch.

19. The catalytic converter of claim 11 wherein the monolith element is wrapped with a layer of ceramic fiber paper which comprises about 93 weight percent ceramic fiber having about a 70/30 fiber-to-shot ratio said ceramic fiber being alumino-silicate glassy fiber having an alumina content of about 50 weight percent said ceramic fiber paper having an installed thickness of about 0.035 inches and an installed density of about 43 pounds per cubic foot and said intumescent layer includes two layers of a material comprising from about 40 to about 65 weight percent unexpanded vermiculite flakes which have been treated in an aqueous ammonium solution to substantially complete the ion exchange with NH4+cations from about 25 to about 50 weight percent inorganic fibrous material and from about 5 to about 15 percent of binder said intumescent layer upon exposure to heat in excess of 350°C undergoing thermal expansion.

20. A method of mounting a gas-pervious ceramic monolith catalyst element having inlet and outlet end faces within a housing comprising the steps of:
a) wrapping a layer of ceramic fiber paper around the monolith between its inlet and outlet end faces;
b) wrapping said ceramic fiber paper layer wrapped monolith with intumescent sheet material to form an assembly; and c) forming a housing around said assembly in which said ceramic fiber paper and intumescent sheet material are radially compressed between said monolith and said housing.