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  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
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Definitions

• Diesel Oxidation Catalyst DOC
• Diesel NOx Trap/NOx Storage Catalyst DNT/NSC
• SCR Selective Catalytic Reduction catalyst
• CO CO
• HC HC
• NOx nitrogen oxides
• the diesel exhaust stream also contains entrained solids, commonly referred to as particulate matter or soot.
• This carbon-based material is a byproduct of incomplete combustion and arises due to heterogeneity of the air-fuel mixture within the cylinder and presents a unique and specific challenge with regards to its control and conversion into environmentally benign products.
• the DPF typically comprises an inert porous ceramic e.g. silicon carbide, cordierite etc. monolith substrate which may be additionally wash-coated with an active catalytic formulation to facilitate the chemistries required of the device e.g. soot combustion, (secondary) emission control, NOx abatement, etc.
• the wash-coat formulation itself is typically a heterogeneous-phase catalyst and may contain particles of highly active precious group metal (PGM) dispersed and stabilized on a refractory oxide support or supports; e.g. alumina.
• PGM highly active precious group metal
• the DPF may additionally contain an Oxygen Storage (OS) component to enhance the regeneration function of the filter.
• OS Oxygen Storage
• the DPF achieves high filtration efficiency of particulates as a result of the physical filtration achieved by forcing the exhaust flow through the porous wall of filter.
• this results in a build up of stored material, commonly referred to as a filter- cake, within the filter which results in an ever increasing back pressure penalty, arising from the work required to force the gas flow through an increasingly dense flow restriction.
• This flow restriction leads to an unacceptable decrease in engine performance and hence, the filter-cake must be combusted in order to 'regenerate' the filter to a near pristine condition such that it is able to again store the carbonaceous particulates with minimal back pressure penalty.
• an electric heater may be employed to generate the heat to initiate the combustion cycle; e.g. US patent 7,469,532.
• the filter is regenerated by a so-called "post-injection" cycle in which secondary fuel is introduced, either by late cylinder injection or via dedicated fuel injection unit in the exhaust train, and the hydrocarbons thus entrained in the exhaust flow are combusted over an oxidation catalyst situated prior to the DPF to generate a transient thermal 'bloom' within the filter which initiates the conversion of the soot into environmentally benign products (CO 2 , H 2 O); e.g. see SAE paper 2008-01-0481 and references therein.
• soot combustion initiated in this manner results in a phenomenon known as 'oil dilution' which can both adversely affect engine operation and result in ash deposition (inorganic salts) within the filter which impact the back pressure, soot capacity and catalytic performance of the filter; e.g. US patent 7,433,776.
• soot combustion initiated in this manner proceeds in a more homogeneous; i.e. non-catalytic manner and can be uncontrolled.
• This process has been denoted as 'de-coupling' of the OS and soot and is the result of the reaction of engine out NO over oxidized PGM to produce NO 2 which combusts the soot in the immediate environment of the catalyst producing CO + NO.
• the NO byproduct of this process is further 'recycled' to NO 2 and the soot combustion re-initiated, again removing only that soot which immediately contacts the catalyst.
• This cycle is the basis of US 4,902,487 and was previously believed to be the major reaction providing low temperature soot combustion/regeneration. However, this mechanism appears only effective at removing low concentrations of soot and indeed only that proportion of soot in direct contact with the catalyst.
• this mechanism effectively 'de-couples' the catalyst and soot and dramatically decreases the effectiveness of the OS-mediated regeneration method and may in fact be considered to be a reactive poison which effectively 'deactivates' the 'true' OS mediated low temperature, passive, soot regeneration reaction required for optimum soot emission control.
• the design of the next generation ion exchanged OS materials has been found to be effective at both circumventing this 'de-coupling' process and also in promotion of the redox characteristics of the OS and hence demonstrated robust performance benefits with respect to soot regeneration on all both the engine dynamometer and in vehicle trials on wash-coated DPFs (see US application no. 12/363,329).
• a significant advance in the development of a method and apparatus for the (semi) continuous, direct catalytic, oxidation of diesel particulate matter may be realised by the combination of base metal modified Oxygen Storage (OS) materials with a conventional flow substrate.
• the substrate is selected from a range of ceramic or metallic technologies upon which the active washcoat is disposed. Such substrates can be metallic parts, ceramic or metal foams.
• the substrate is further characterised by presenting a high number of channels or cells per unit area or by the ability to introduce turbulent flow due to the construction of its internal flow channels.
• the particular combination of the base metal modified OS direct soot oxidation catalyst with the flow through monolith provides a synergy which enables high conversion of particulate matter without the backpressure penalty introduced by the conventional DPF.
• the synergy is believed to arise from the ability of the active OS to combust soot at lower temperatures which in turn is facilitated by the decreased thermal mass of the conventional substrate, with the latter still providing sufficient geometric surface area for soot deposition and reaction.
• This provides for the large improvements in lower temperature activity and is in marked contrast to the conventional wall flow DPF wherein large thermal mass of the substrate, particularly for SiC DPF, inhibits initiation and especially propagation of soot combustion.
• this combination of technologies provides a means for the effective conversion of particulate matter under conditions more typical of the standard driving cycle i.e. soot combustion without recourse to high temperature active regeneration cycles and the various penalties and other issues associated thereto.
• the doped OS materials herein are based upon ZrO 2 /CeO 2 solid solutions containing a substantially phase pure cubic fluorite structure and are produced by the specific ion exchange of base i.e. non-precious group metals.
• the range of appropriate materials and full details regarding execution of the ion exchange are described in US application nos. 12/363,310 and 12/363,329.
• the mode of ion exchange essentially involves the introduction of active metal/ cations into the solid solution under chemically basic, i.e. conditions of high pH, that is say high OHVlow hydronium (H 3 O + ) or proton (H + ) content.
• the resultant materials demonstrate high activity and hydrothermal durability in contrast to any promotion realized by conventional impregnation of an acidic metal e.g. metal nitrate, where formation of bulk oxide phases in fresh materials and rapid sintering of such oxide phases, with resultant deactivation, is the norm.
• the proposed exchange of the H + species, present at Ce 3+ defect sites within the Ce-ZrOx lattice, by metal ions enables the incorporation and stabilization of specific mono-valent e.g. K + , di-valent e.g. Cu 2+ , tri-valent e.g. Fe 3+ and higher valence ions at high dispersion within the oxide matrix.
• base metals thus incorporated is based upon oxides known to be active for reactions of especial interest or catalytic importance.
• Metals of specific catalytic significance include Ag, Cu, Co, Mn, Fe, alkali metals, alkaline earth metals or transitions metals, or other metal or metalloid known to form a stable nitrate which can undergo subsequent decomposition and reduction N 2 under conditions within the conventional operational window of the vehicle exhaust.
• transition metal refers to the 38 elements in Groups 3 to 12 of the Periodic Table of Elements.
• high cell density / turbulent flow through monoliths is also required to provide sufficient interaction and subsequent reaction between the entrained soot particles within the exhaust flow and the active catalytic coating.
• the term high cell density is consistent with preformed flow through monolith substrates with a large (> 600) number of individual cells of flow channels per square inch. It is proposed that this high cell density firstly introduces turbulence at the inlet to maximise possible soot collisions with the active wash- coated walls of the monolith. Secondly, the high cell density restricts the flow path through the monolith, again increasing the potential for particulate collisions and retention/reaction on the active wash-coat, but without the large backpressure penalties associated with the conventional DPF.
• the use of the flow-through substrate removes existing constraints regarding total washcoat loading, or the use of layered technologies with specific functionalities, e.g. soot combustion catalyst in one layer (overcoat) and SCR catalyst in a second layer (undercoat), equally it enables the use of an undercoat rich in Al 2 O 3 to provide high washcoat adhesion, but with low intrinsic catalytic function, onto which a second pass containing all required OS, PGM and NOx trap etc. active components may be dispersed.
• the overcoat would under normal conditions present lower adhesion and would conventionally be diluted with binder, e.g.
• the incorporation of binder results in a decrease in activity due to dilution of the active phase, hence the layered design is preferred.
• This layering ensures the surface coating that would interact/react with the soot as it passed through the flow-through substrate would exclusively consist of active material and would therefore maximize catalytic action.
• the enabling of higher washcoat loads when using the flow through monolith also provides the capability of employing higher concentrations of active materials to be coated on the substrate thereby further enhancing the performance and hydrothermal durability of the technology without the catastrophic back pressure penalty such an approach would present using the conventional DPF.
• the flow through substrate washcoat load could be increased from 10 g/1 to 180 g/1 or higher concomitantly increasing the effective geometric surface area for catalyst to soot contact to again increase in combustion efficiency.
• the textural characteristics of the washcoat e.g. particle size, roughness etc. may be optimised for activity rather than merely to minimize back pressure penalty.
• Conventional formulations for DPFs typically target a D 5 o (diameter of particle at 50%) value of 5 microns or less to enable 'in-wall' coating, i.e. coating of the internal porosity of the substrate without formation of a discrete washcoat layer on the surface of monolith, in order to minimize backpressure penalty.
• Such a particle size distribution is typically achieved by aggressive milling of the raw materials used in the washcoat.
• CeOx or CeZrOx containing oxide solid solutions for soot oxidation have been widespread.
• conventional CeZrOx solid solutions as typically employed in three-way catalysts, typically exhibit a redox maximum, as determined by H 2 Temperature Programmed Reduction (TPR) at ca. 600 0 C.
• TPR H 2 Temperature Programmed Reduction
• This imposes the requirement for high exhaust gas/reaction temperatures in the application in order for the OS material to provide the maximum "buffering" or oxygen donation benefit.
• this requirement for high temperature to access the active lattice oxygen is a barrier to the implementation of CeZrOx for lower temperature direct soot oxidation.
• OS materials are typically "promoted” by the addition of a Precious Group Metal (PGM) component, e.g. Pt, Pd or Rh.
• PGM Precious Group Metal
• Pt Precious Group Metal
• Rh a Precious Group Metal
• promotion by these metals contributes a large additional cost to the price of the emission control system.
• PGM especially Pt, promotes the 'classical' chemistry of NOx-mediated soot oxidation as described in US 4,902,487.
• Many data available to date are consistent with as little as only ca. 50% of the total Ce IV available undergoing reduction. At this time it is uncertain whether this is due to a fundamental issue, or due to limitations with the current synthetic method(s) employed in the manufacture of the OS material leading to a mixed Ce IV/Ce III valency or whether a combination of additional chemical, structural or textural limitations are responsible.
• OS materials provide only limited, if any, additional synergies to the emission control system.
• ideal material components provide additional integrated chemical mechanisms to further enhance emissions control, e.g. NOx scavenging and reduction to N 2 .
• OS materials are key components in realising highly active and materials present significant limitations to development of the next generation of exhaust catalyst that will be required to comply with newer and ever more stringent emission targets. What is required is a new class of OS materials that are active at lower temperatures, especially the Cold Start portion of vehicular applications to promote catalytic function. These OS materials should also display high hydrothermal durability and be tolerant to potential exhaust poisons in order to enable their use in the wide range of demanding exhaust environments.
• FIG 1 shows a schematic of the synthetic gas bench (SGB) reactor in which the concept trials were executed.
• a monolith core using a flow through washcoated monolith with 400 or 900 cell per square inch-CPSI
• quartz sleeve packed with quartz wool were placed in the stainless steel reactor as shown.
• the temperature, pressure drop and O 2 content of the reactor were monitored using the respective probes positioned as shown in Figure 1.
• Representative sampling of the gaseous reaction byproducts was performed by on-line mass spectrometry with appropriate corrections for m/z overlaps.
• Phase 1 Soot loading cycle hi this portion of the experiment
• Printex U soot analogue obtained from Evonik Degussa
• the fluidized bed unit contains the soot material and a flow of N 2 is based through the base of the bed to establish the fluid condition and thus entrain suspended solid material with the gas flow.
• the N 2 /soot flow is then mixed with the reactive gas leg and passes through the reactor, where soot deposition in the monolith may occur.
• the rate of soot delivery is 0.2 g/hour under typical loading conditions, hi order to retain any soot passing through the flow through monolith, i.e. determine soot 'slip' or low filtration efficiency, a bed of quartz wool was packed in the outlet position of the reactor.
• Phase 2) Regeneration The sample is purged with dry N 2 and then heated in N 2 / O 2 (as a TPO or Temperature Programmed Oxidation) or reactive gas mixture (as described in Figure 3) to 750°C and the reactor conditions e.g. back pressure, O 2 content, temperature and off gas monitored.
• N 2 / O 2 as a TPO or Temperature Programmed Oxidation
• reactive gas mixture as described in Figure 3
• any soot trapped in the quartz wool is also combusted during the regeneration but only at high temperatures via the conventional homogeneous combustion pathway, this turn enables a determination of soot 'slip' through the monolith and thus determine the impact of cell density on trapping efficiency.
• An important note is made herein in that prior to any performance testing the various monolith cores were stabilised with respect to performance/aged, this being achieved by an in-situ thermal treatment at 750°C for four hours.
• Figure 3 outlines the various gas compositions employed during the loading and regeneration trials.
• Reactive gas for example, refers to a gas composition containing N 2 , O 2 , CO, NO and propene in the concentrations listed in line 3.
• FIG. 4 compares the back pressure (hereafter B.P.) response for a 400 CPSI (cells per square inch) flow through monolith during a three hour (10800 s) soot loading cycle as a function of either gas environment during loading or temperature and gas environment.
• B.P. back pressure
• TPO is consistent with the B.P. response trends seen during soot loading ( Figure 4).
• TPO after the loading cycle at 200°C in N 2 / O 2 results in a CO 2 evolution profile with three features, a small oxidation feature at between 250-350°C, ascribed to catalytic combustion of soot and two large CO 2 features at 640°C, due to filter cake combustion, and at >700°C ascribed to the combustion of soot 'slip' i.e. soot that passed through the monolith and was trapped in the quartz wool 'filter' toward the outlet of the reactor.
• Figure 6 compares the O 2 concentrations at the reactor outlet during the TPO cycles described in Figure 5.
• the data reflects the same trends noted above with decreased O 2 consumption being recorded for reactive gas soot loading cycles and for soot loading cycles at 250 and 300°C.
• This peak is ascribed to the desorption of NO/NO 2 from the catalyst and will be examined in more detail in later figures (see Figures 9, 11, 13, 14, 15, 16 and 18b). Note, due to the positioning of the O 2 sensor at the outlet of the monolith there is no O 2 consumption recorded for the high temperature soot 'slip' event.
• FIG. 8 A comparison of the subsequent TPO reactions after the loading cycle of Figure 7 is shown in Figure 8.
• the data show a clear change in the effectiveness of the technology as a function of cell density.
• the 900 CPSI substrate shows a dramatic improvement in soot filtration efficiency, with only very small CO 2 evolution features seen for both filter cake and 'slip' combustion events.
• the sample also exhibits an increased efficiency with the direct catalytic oxidation feature, hence peak CO 2 production from direct catalytic oxidation is now observed at ca. 240 0 C versus ca 300-310°C for the 400 CPSI monolith.
• Figure 11 displays the B.P. response and O 2 consumption traces associated with the TPO cycles described in Figure 10. hi all cases the data sets are consistent with the observed CO 2 production profiles. Hence, in all cases, CO 2 evolution/residual soot combustion is associated with O 2 consumption and with a net decrease in B.P. as the monolith channels are cleaned of the restrictive soot particles. The extent of O 2 consumption follows the net CO 2 production i.e. 100> 150> 200°C. Again, all samples the secondary NOx related feature at 475°C.
• the B.P. responses also appear to reflect the conditions of soot loading with the 'relaxation' response being sharpest for the 200 0 C cycle, then 150°C and finally 100°C loading cycle, again consistent with the residual soot retention for the various tests.
• Figure 12 shows an example of a temperature programmed soot loading using a 900 CPSI monolith.
• This test there was simultaneous soot loading cycle in full reactive gas mixture with heating of the sample from 100°C to 200 0 C.
• the data shows the expected CO (and propene) light-off curves, which were again found to be coincident with soot combustion, as reflected in the peak then decay seen for CO 2 production and O 2 consumption traces.
• Figure 13 shows a temperature programmed reaction experiment performed after the temperature programmed reaction soot loading in Figure 12.
• the protocol for this test entailed cooling the sample in-situ to 100°C in flowing N 2 , after the soot loading cycle was completed, upon stabilisation at 100 0 C, the full reactive gas mixture was then reintroduced, and the sample heated to 750°C, per standard method.
• the data shows the expected light-off of CO (propene also undergoes light-off but the signal is omitted for clarity with CO, NO and NO 2 traces) as evidenced by the responses in CO, CO 2 and also the O 2 sensor. Interestingly, there is again a peak of CO 2 production at ca.
• any NO 2 that is generated which would normally result in 'de-coupling' of catalyst-soot contact is trapped on the highly dispersed Ag centres and retained to high temperatures where it is released in the plume observed.
• the plume of desorbed NOx then may react with any traces of soot remaining on the part, particularly any species that are spatially distant from the catalyst surface i.e. with 'poor' contact.
• FIG 14 shows the TPO results for the 900 CPSI monolith after a soot loading with reactive gas and temperature ramp, as per Figure 12.
• the TPO protocol there are no light-off features but rather a series of peaks due to the various phenomena occurring over the catalyst versus temperature. Firstly there is a CO 2 production peak, attributed to the combustion of residual retained soot. This peak is centred at 300°C, ca. 75°C higher than in the temperature programmed reaction case.
• Figure 16 shows a TPO performed subsequent to the loading cycle of Figure 15.
• there are no significant reaction or desorption events evident hi particular, there is no additional CO 2 production, no high temperature soot 'slip' phenomenon, i.e. the data is consistent with complete conversion of any soot loaded during the loading cycle, further confirming the high effectiveness of the technology.
• Figure 17 contrasts reactive gas loading cycles, with temperature ramp (100-200 0 C) under the standard GHSV of 15000 h "1 versus a GHSV of 25000 h "1 (versus monolith volume). It is emphasised at this point that the soot delivery rate in both tests as determined by the flow rate through the fluidised bed was constant in both cases and the increase in GHSV was achieved by increasing the flow rates of the various gases within the reactive gas manifold. Analysis of the subsequent data from both tests show comparable response with response to gas phase chemistry, with CO (and HC) light-off being unaffected, as evidenced by the comparable CO 2 responses.
• the soot oxidation follows the same profile as the lower GHSV case and there is simply an increase in the net CO 2 production. This is also reflected in the B.P. responses with the sample loaded under high GHSV showing a more rapid and larger B. P. 'relaxation' than the sample loaded under lower GHSV. Similarly the NOx evolution response is larger for the high GHSV sample, reflecting the higher mass fraction of NOx exposure during the test. This in turn results in the small differences in apparent O 2 consumption, as recorded by the O 2 sensor.
• the impact is not catastrophic and the monolith retains its ability to either combust or trap all soot at lower temperatures and then to facilitate its combustion at temperatures still within the normal operating window of a conventional vehicle, i.e. the system still provides effective soot filtration and combustion without recourse to conventional active regeneration strategy.
• the present invention relates to a method and apparatus for the continuous/semi-continuous direct catalytic, oxidation of diesel particulate matter by the combination of base metal modified Oxygen Storage (OS) materials in association with turbulent flow / high cell density flow through monoliths.
• OS Oxygen Storage
• the particular combination of the base metal modified OS direct soot oxidation catalyst with the flow through monolith provides a synergy which enables high conversion of particulate matter without the backpressure penalty introduced by the conventional DPF. It is believed that the synergy arises from the ability of the active OS material to combust soot at lower temperatures than in conventional systems, which in turn is facilitated by the decreased thermal mass of the conventional substrate, with the latter still providing sufficient geometric surface area for soot deposition and reaction.
• the present invention represents a significant advance in the development of a method and apparatus for the (semi) continuous, direct catalytic, oxidation of diesel particulate matter may be realized by the combination of base metal modified Oxygen Storage (OS) materials with a conventional flow substrate.
• the substrate is selected from a range of ceramic or metallic technologies upon which the active washcoat is disposed. Such substrates can be metallic parts, ceramic or metal foams.
• the present invention relates to a synergistic combination of a catalyst and a substrate for the filtration and continuous, direct catalytic, oxidation of diesel particulate matter at low temperatures.
• the catalyst comprises catalytically active precious metal (Pt, Pd, Rh or combinations thereof), a host cerium-based solid solution which is a substantially phase pure cubic fluorite (as determined by x-ray diffraction method) of the CeZrOx type which is well known in the art and a refractory oxide support, e.g. ( ⁇ )Al 2 O 3 , ZrO 2 or other known oxide support.
• the CeZrOx is further modified by the incorporation of an active base metal, e.g.
• the catalyst further comprises a monolith substrate, of conventional design, wherein the monolith is an inert ceramic or metal substrate upon which the active catalyst formulation/ washcoat is disposed.
• the monolith substrate is further characterised by a high cell density, i.e. a large number of active channels per unit area, for effective synergy a value of > 600 cells per square inch.
• the active washcoat may be applied to the perforated, punched and embossed metal foils (e.g. TS, LS, PE and MX type systems; see for example US patent 6,689,327) with beneficial effect.
• the combined active washcoat and monolith system may be applied to the challenge of particulate emission control catalysts for diesel (or other fuel lean) or potential gasoline (stoichiometric) application.
• the particular example described herein is for the application of these materials in the area of continuous, direct catalytic oxidation of diesel particulate matter upon its interaction with the high cell density substrate.
• the solid solution contains a cationic lattice with a single-phase, as determined by standard x-ray diffraction method. More preferably this single-phase is a cubic structure, with a cubic fluorite structure being most preferred. Additionally, it is noted that the doping process may be performed without formation of an additional bulk phase, as determined by XRD.
• the OS material may include those OS materials disclosed in US patents 6,585,944; 6,468,941 ; 6,387,338 and 6,605,264 which are herein incorporated by reference in their entirety.
• the flexibility of the basic exchange provides for the modification of all current known cerium oxide and Ce- Zr-based solid solution materials to be thusly modified and enhanced.
• the OS materials modified by the doping method shall preferably be characterized by a substantially cubic fiuorite structure, as determined by conventional XRD methods.
• the percentage of the OS material having the cubic structure, both prior and post exchange, is preferably greater than about 95%, with greater than about 99% typical, and essentially 100% cubic structure generally obtained (i.e. an immeasurable amount of tetragonal phase based upon current measurement technology).
• the exchanged OS material is further characterized in that it possess large improvements in durable redox activity with respect to facile oxygen storage and increased release capacity e.g. as determined by H 2 Temperature Programmed Reduction (TPR) method.
• TPR H 2 Temperature Programmed Reduction
• an active soot oxidation catalyst comprising a precious group metal or metals (Pt, Pd, Rh and combinations thereof), a base metal doped cerium-oxide containing solid solution and a refractory oxide carrier all of which together are employed as a coating, e.g., disposed on/in an inert substrate or carrier, the substrate or carrier being characterized by a high number of channels or cells per unit area or by the its ability to introduce turbulent flow due to the construction of its internal flow channels.
• Exhaust gas treatment devices can generally comprise housing or canister components that can be easily attached to an exhaust gas conduit and comprise a substrate for treating exhaust gases.
• the housing components can comprise an outer "shell", which can be capped on either end with funnel-shaped 'end-cones' or flat 'end-plates', which can comprise 'snorkels' that allow for easy assembly to an exhaust conduit.
• Housing components can be fabricated of any materials capable of withstanding the temperatures, corrosion, and wear encountered during the operation of the exhaust gas treatment device, such as, but not limited to, ferrous metals or terrific stainless steels (e.g., martensitic, terrific, and austenitic stainless materials, and the like).
• a retention material Disposed within the shell can be a retention material ("mat” or “matting”), which is capable of supporting a substrate, insulating the shell from the high operating temperatures of the substrate, providing substrate retention by applying compressive radial forces about it, and providing the substrate with impact protection.
• the matting is typically concentrically disposed around the substrate forming a substrate/mat sub-assembly.
• Various materials can be employed for the matting and the insulation. These materials can exist in the form of a mat, fibres, preforms, or the like, and comprise materials such as, but not limited to, intumescent materials (e.g., a material that comprises vermiculite component, i.e., a component that expands upon the application of heat), non-intumescent materials, ceramic materials (e.g., ceramic fibers), organic binders, inorganic binders, and the like, as well as combinations comprising at least one of the foregoing materials.
• intumescent materials e.g., a material that comprises vermiculite component, i.e., a component that expands upon the application of heat
• non-intumescent materials e.g., ceramic materials that comprises vermiculite component, i.e., a component that expands upon the application of heat
• ceramic materials e.g., ceramic fibers
• Non- intumescent materials include materials such as those sold under the trademarks "NEXTEL” and “INTERAM 1101HT” by the “3M” Company, Minneapolis, Minnesota, or those sold under the trademark, "FIBERFRAX” and “CC-MAX” by the Unifrax Co., Niagara Falls, New York, and the like.
• Intumescent materials include materials sold under the trademark "INTERAM” by the “3M” Company, Minneapolis, Minnesota, as well as those intumescent materials which are also sold under the aforementioned "FIBERFRAX” trademark.
• the substrates or carrier employed in this invention can comprise any material designed for use in a spark ignition or diesel engine environment having the following characteristics in addition to the high cell density/turbulent flow requirement stated previously: (1) capability of operating at temperatures up to about 600°C and up to about l,000°C for some applications, depending upon the device's location within the exhaust system (e.g., manifold mounted, close coupled, or underfloor) and the type of system (e.g., gasoline or diesel); (2) capability of withstanding exposure to hydrocarbons, nitrogen oxides, carbon monoxide, particulate matter e.g. soot and the like, CO 2 , and/or sulfur; and (3) have sufficient surface area and structural integrity to support a catalyst, if desired.
• the exhaust system e.g., manifold mounted, close coupled, or underfloor
• the type of system e.g., gasoline or diesel
• hydrocarbons, nitrogen oxides, carbon monoxide, particulate matter e.g. soot and the like, CO 2 , and/or
• Some possible materials include cordierite, silicon carbide, metal, metal oxides; e.g. alumina and the like, glasses and the like, and mixtures comprising at least one of the foregoing materials.
• Some suitable inert ceramic materials include 'Honey Ceram', commercially available from NGK-Locke, Inc, Southfield, Michigan, and 'Celcor', commercially available from Corning, Inc., Corning, New York. These materials can be in the form of foils, perform, mat, fibrous material, monoliths e.g.
• porous structures e.g., porous glasses, sponges, foams, pellets, particles, molecular sieves, and the like (depending upon the device), and combinations comprising at least one of the foregoing materials and forms, e.g., metallic foils, open pore alumina sponges and porous ultra- low expansion glasses.
• these substrates can be coated with oxides and/or hexaaluminates, e.g. stainless steel foil coated with a hexa-aluminate scale.
• the substrate can have any size or geometry, within the previously defined limits, the size and geometry are preferably chosen to optimize surface area in the given exhaust gas emission control device design parameters.
• the substrate has a honeycomb geometry, with the combs through-channel having any multi-sided or rounded shape, with substantially square, triangular, pentagonal, hexagonal, heptagonal, or octagonal or similar geometries preferred due to ease of manufacturing and increased surface area.
• the exhaust gas treatment devices can be assembled utilizing various methods. Three such methods are the stuffing, clamshell, and tourniquet assembly methods.
• the stuffing method generally comprises pre-assembling the matting around the substrate and pushing, or stuffing, the assembly into the shell through a stuffing cone.
• the stuffing cone serves as an assembly tool that is capable of attaching to one end of the shell. Where attached, the shell and stuffing cone have the same cross-sectional geometry, and along the stuffing cone's length, the cross-sectional geometry gradually tapers to a larger cross-sectional geometry. Through this larger end, the substrate/mat sub-assembly can be advanced which compresses the matting around the substrate as the assembly advances through the stuffing cone's taper and is eventually pushed into the shell.
• Exhaust gas treatment devices comprising the doped solid solutions can be employed in exhaust gas treatment systems to provide both an active soot combustion catalyst but also a NOx adsorption function, and thus specifically reduce a concentration of undesirable constituents in the exhaust gas stream.
• an exemplary catalyst system can be formed utilizing the doped OS as a catalyst component, wherein the catalyst system is disposed on a substrate, which is then disposed within a housing. Disposing the substrate to an exhaust gas stream can then provide at least a NOx storage function, and desirably even reduce the concentration of at least one undesirable constituent contained therein.
• the catalyst does not conform the standard architecture of a CDPF or Diesel NOx Particulate Trap and hence does not comprise a porous substrate having alternating channels. Rather the preferred configuration of the catalyst is as a conventional 'flow through 1 monolith, of high unit cell count per unit area, upon which is disposed the active catalyst washcoat. The combination of the active washcoat with the high internal surface area and turbulent deposition mechanism is sufficient to facilitate retention and continuous particulate oxidation under conventional operating temperatures and flows of a diesel/compression ignition vehicle.
• a second combined heat transfer and catalyst activation component is arises from the activation of the redox oxide arising from its participation in the CO oxidation process. It has been shown that the doped cerium oxides are effective oxidation catalysts, even in the absence of PGM, and can facilitate CO oxidation at low temperatures (DP-316440). In doing so the catalyst O ion transport function is activated, and energy released at the active site of CO oxidation. The subsequent re-oxidation of the depleted oxygen results in a further exotherm, distributed throughout the entire structure of the OS, in a sense further priming the OS to initiate soot oxidation. This mechanism forms part of the basis of US 2005/0282698 Al, wherein a fuller explanation may be found.
• OS 40% CeO 2 ; 50% ZrO 2 /HfO 2 ; 5% La 2 O 3 ; 5% Pr 6 O n

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