WO2009137110A1

WO2009137110A1 - Treatment of internal combustion engine exhaust using immobilized ceramic fiber materials

Info

Publication number: WO2009137110A1
Application number: PCT/US2009/002898
Authority: WO
Inventors: Gary Lee Carson; John Murray Finley
Original assignee: Gary Lee Carson; John Murray Finley
Priority date: 2008-05-09
Filing date: 2009-05-11
Publication date: 2009-11-12

Abstract

Immobilized ceramic nanofibers, ceramic microfibers, or a combination of ceramic nanofibers and microfibers with and without embedded catalyst particles, or catalyst coatings on a rigid or fibrous support structures, permeable or non-permeable, manufactured from ceramic, metallic, or ceramic metallic composites for the destruction of nitrogen oxides (NO_x), sulfur oxides (SO_x), and carbon monoxide (CO) gaseous components and the capture and oxidation of soot particles and other hydrocarbon (HC) constituents, methane and non-methane hydrocarbon materials, from internal combustion engine exhaust sources defined to include non-road and on-road, spark-ignition 2- cycle and 4-cycle engines, non-spark ignition engines, and handheld (HH) and non-handheld (NHH) engines.

Description

TREATMENT OF INTERNAL COMBUSTION ENGINE EXHAUST USING IMMOBILIZED CERAMIC FIBER MATERIALS

CROSS REFERENCE

[0001] This application claims priority from U.S. Provisional Application Serial No .61/127, 015 filed on May 9, 2008 which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention described herein relates to catalytic systems for the treatment of gaseous and particulate components from internal combustion engine exhaust to destroy nitrogen oxides (NO_x) , sulfur oxides (So_x) and carbon monoxide (CO) gaseous components and the capture and oxidation of soot particles and other hydrocarbon (HC) constituents, methane and non-methane hydrocarbon materials.

BACKGROUND OF THE INVENTION

[0003] Heterogeneous catalyst materials and mediums thereof are commonly used in the post-treatment of effluent gases from combustion processes. These catalyst materials convert toxic combustion by-products including gaseous and particulate pollutants into less-toxic substances. To date, virtually all catalytic devices have been constructed from ceramic substrates or stainless steel foils in the shape of a solid monolithic structure, for example a "honeycomb" structure. For the past two decades, these materials have been optimized for use in the automotive and large engine (including diesel engines) market sectors. However, to date, conventional catalytic devices have not been extensively developed to include nor have they been readily accessible for small engine applications due to technical limitations, size issues, weight constraints, and additional performance requirements dictated by these engine types.

[0004] As a requirement for new advanced catalytic mediums, the USEPA has clearly stated that the only viable methods to meet current and future pollution reduction requirements for small off-road engines will include improved combustion chamber design, utilization of exhaust gas recirculation (EGR) , enleanment, thermal oxidation by air injection, and the use of advanced, high-temperature catalyst materials. These technical requirements pose critical technical hurdles since pollution reduction strategies for small internal combustion engines involve some unique engineering and safety perspectives as well as cost constraints. Solving these technical hurdles and challenges will also produce improvements that can be applied to larger internal combustion engines (>19 kW) .

[0005] Providing solutions for small engine exhaust treatment is important since the EPA anticipates that the emitted nitrogen oxides (NO_x) , hydrocarbons (HC) , carbon monoxide (CO), and particulate matter (PM) from small to medium sized internal combustion engines (< 19 kW) are significant. The EPA estimates that small gasoline engines (Class 1 through Class V) with engine displacement from less-than 20cc to over 225cc account for greater than 25% of total nationwide HC emissions and 30% of total nationwide CO emissions. This is not surprising considering the fact that the estimated number of walk-behind mowers and ride lawn and turf equipment (Class I and Class II engines) in-use throughout the US exceeds 47 million with an additional 14 million new Class I and Class II engines manufactured each year. In addition to these non-road engines, internal combustion engines used to power small on-road vehicles (for example motorcycles) and marine craft produce significant amounts of atmospheric gaseous and particulate pollutants.

[0006] Current methods employed in both small (<19 kW) two-stroke and four-stroke SI engines to meet EPA standards include optimizing air-fuel mixture ratios, combustion chamber modifications, advanced fuel metering systems, and limited exhaust aftermarket technologies. Generally, two- stroke engines have much higher emissions of HC due to short-circuiting of raw fuel and somewhat lower emissions of NO_x due to lower combustion temperatures with both engine types having similar CO emissions. However, even for small 4-stroke engines, HC, CO, and NO_x emissions are higher compared to conventional on-road gasoline engines because small non-road engines are operated at higher air/fuel ratios (typically 12:1) to prevent overheating during operation. Although enleanment can be used to decrease HC and CO, NO_x tends to increase so that the overall change in HC+NO_X, which is regulated as a combination, may not be significant. Although studies have indicated that EGR can be successful in reducing total HC+NO_X and CO emissions from Class I and Class II engines, new Phase 3 standards will be difficult to meet using EGR combined with enleanment strategies. Anticipated technologies to effectively perform under these unique conditions will require multiple strategies in combination to meet the proposed standards with post treatment of exhaust streams (i.e. filter and catalyst devices) integrated into most solutions.

[0007] The combined high concentration of HC and CO in exhaust streams from Class I and Class II engines poses a current problem for most catalyst systems because if combined with sufficient quantities of air, temperature within the catalytic chamber can exceed the temperature limits of the catalyst leading to accelerated catalyst loss and deactivation due to agglomeration of catalyst materials. Since most new Class I and Class II engines will operate at low fuel/air ratios or employ supplemental air injection to reduce HC and CO emissions producing a net oxidizing exhaust environment increase in NO_x. Ultimate reduction requires innovative catalyst system design. Post treatment technologies of these exhaust sources is limited due to space constraints leading to solutions that need to be compact and efficient. The EPA estimates that for Class I and Class II engines using advanced catalyst control strategies, the total size of the catalyst substrate volume needs to be between 10 to 25% of the engine cylinder displacement. Based upon these facts, a method for reducing HC, PM, NO_x, and CO emissions from small engines incorporating a compact, efficient catalytic/filter device that has a catalyst substrate volume of approximately 10 to 30cc for Class I engines and approximately 50 to 200cc for Class II engines is required.

[0008] Traditional catalytic devices have proven to be problematic when applied to small engine applications due to size and weight issues, as well as long-term longevity problems. However, not all performance issues of conventional catalytic mediums are limited to small engine applications. The limitations of conventional catalyst delivery systems for internal combustion engine treatment are also due to the physical nature of the catalytic medium. Virtually all catalytic configurations utilize the monolithic structure, either ceramic or metallic, as a support medium for catalytic materials. Catalyst materials are applied to these supports by a process termed "wash coating" by which a coating of ceramic material, promoters and catalyst particles are formed on the surfaces of the support structure. Single or multiple wash coats can be applied to a given support structure depending on the application and the targeted catalytic reactions. Multi- layered wash coatings are used to promote separate, different catalytic reactions within the wash coat. For example, the top layer may catalyze CO and hydrocarbons in the presence of oxygen, while a bottom layer - with respect to gas flow - may be designed for NO_x reduction which is favorable in the absence of oxygen.

[0009] A significant limitation of current catalytic mediums is that at high operational temperatures, i.e. greater than approximately 1,110⁰F (600⁰C), the catalyst particles within the "wash coat" tend to agglomerate into larger particles therein decreasing the available catalyst surface area available for pollutant conversion. An additional change that decreases catalytic performance is a decrease in porosity of the wash-coat structure which limits gas and contaminant flow to the catalyst materials and possible degradation of the support structure - mainly a concern for cordierite materials that have a fusion temperature around at 1,500⁰F (820⁰C) . These are concerns for larger-engines but are critical when considering catalytic devices for small engines since temperatures within the catalytic device can exceed 1,830⁰F (1, 000⁰C) , due to higher amounts of fuel materials reaching the catalyst structure since these engines are operated under rich-burn conditions .

[0010] Advanced, thermally stable catalyst support structures and catalyst materials operated at high application temperatures , greater-than 1,110⁰F (600⁰C) are required not only for small engine applications (<19 kW) but also for providing enhanced catalytic devices with improved performance and cost reductions for larger engine applications .

SUMMARY OF THE INVENTION

[0011] The principal feature of the present invention is the use of immobilized ceramic fibers such as ceramic nanofibers and/or ceramic microfibers, with and without embedded metal catalyst particles, or catalytic coatings for use in the treatment of gaseous exhaust from internal combustion engines. These gaseous exhausts include those emitted from non-road and on-road, spark-ignition 2-cycle and 4-cycle engines, non-spark ignition engines, and handheld (HH) and non-handheld (NHH) engines.

[0012] In the present invention there is an arrangement integrating either self-supported or secondary supported, ceramic, metallic, or composite media utilizing ceramic nanofibers, ceramic microfibers, or a combination of ceramic nanofibers and microfibers, with and without embedded catalyst materials, or catalytic coatings that can be incorporated into a new catalyst/filter muffler combinations or retrofitted into existing, conventional internal combustion engine designs for the removal of hydrocarbon (HC) materials, particulate material (PM) , nitrogen oxides (NO_x) , sulfur oxides (SO_x) , and carbon monoxide (CO) from engine exhaust sources.

[0013] A further embodiment of the present invention is a system utilizing ceramic nanofiber/microfiber composites, metallic forms and supports, extruded and formed ceramic materials, or a combination of materials for particulate material (PM) removal and/or oxidation, for the capture, or removal, or catalytic destruction of particulate material

(PM), nitrogen oxides (NO_x), sulfur oxides (SO_x), hydrocarbons (HC) , and carbon monoxide (CO) from internal combustion engine exhaust sources.

[0014] Another feature of the present invention is catalyzed ceramic nanofibers, utilizing a blend of ceramic nanofibers having dispersed metallic catalytic materials partially exposed and/or embedded within a ceramic nanofiber structure covering from 1% to 90% of the ceramic nanofiber external and internal surface area, immobilized on ceramic, metallic, or ceramic/metallic composite structures with various configurations including, but not limited to, extruded materials, fibrous materials, and foil/plate-like material structures.

[0015] In addition in accordance with the present invention, ceramic nanofibers and/or ceramic microfibers with and without catalytic materials, can be immobilized by attachment to an inert support structure with or without intermediate conditioning layers and immobilized by attachment and entrainment within a porous or non-porous, fibrous structure. In each immobilization method, the support structure can be either permeable of non-permeable depending on the application.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. IA and FIG. IB illustrate two distinct composite structures. The structure shown in Fig. IA is produced by integrating ceramic nanofibers including the utilization of a ceramic fiber coating placed on the surface of an inert support structure produced from ceramic, metallic or a combination of ceramic/metallic materials, whereas the structure shown in ^'FIG. IB includes the formation of a ceramic nanofiber/microfiber matrix. Both structures provide a mechanism of ceramic fiber immobilization. The ceramic fiber material can be catalyzed with various catalyst substances.

[0017] FIG. 2A and FIG. 2B illustrate two application strategies of ceramic nanofiber/microfiber composite materials for PM and HC removal/oxidation at one level and a single layer of catalyzed ceramic nanofiber/microfiber composites with mixed catalyst composite material at a second level as shown in FIG. 2A and multiple individual catalyst layers of catalyzed ceramic nanofiber/microfiber composite materials used in sequence as shown in FIG. 2B to enhance oxidation of HC, reduction of NO_x and SO_x, and destruction of CO.

[0018] FIG. 3A and FIG. 3B illustrate two possible configurations for immobilizing ceramic nanofibers and ceramic microfibers, alone or in combination, on a non- permeable or permeable support structure constructed from ceramic, metallic, or a combination of ceramic/metallic composite materials. Gas flows over the non-permeable coated support structure in FIG.3A while gas can flow through the permeable support structure in FIG. 3B.

[0019] FIG. 4A and FIG. 4B illustrate rigid support structures for the immobilization of ceramic nanofibers and ceramic microfibers. Rigid support structures can include innovative ceramic structures that provide unique channel geometries to traditional extruded, monolithic ceramic, metallic, or a combination of ceramic/metallic materials with multiple channel configurations including square, round, hexagonal, and trapezoidal openings. Exposed surfaces within the support structure can be coated with ceramic nanofibers, ceramic microfibers and ceramic nanofiber/microfiber combinations and multiple layers for particulate removal and chemical reactions, primarily catalytic reactions involving gaseous constituents.

[0020] FIG. 5 illustrates a fibrous support structure for the immobilization of ceramic nanofbers wherein different mass ratios of ceramic nanofibers and ceramic microfibers can be utilized to enhance particulate removal performance or catalytic performance.

[0021] FIG. 6 illustrates a catalyst delivery system using ceramic nanofiber/microfiber composite material for PM and HC removal/oxidation and a mixed catalyzed ceramic nanofiber/microfiber composite for oxidation of HC, reduction of NO_x and SO_x, and destruction of CO. [0022] FIG. 7 illustrates another catalyst delivery system using ceramic nanofiber/microfiber composite material for PM and HC removal/oxidation and a mixed catalyzed ceramic nanofiber/microfiber composite for oxidation of HC, reduction of NO_x and SO_x, and destruction of CO.

DETAILED DESCRIPTION OF THE INVENTION

[0023] As illustrated in FIG. IA and FIG. IB, ceramic nanofibers, ceramic microfibers, or a combination of ceramic nanofibers and microfibers, with or without embedded catalyst particles, or catalyst coatings are immobilized on permeable or non-permeable ceramic, metallic, or ceramic metallic composite structures for use in the treatment of gaseous exhaust emissions from internal combustion engines defined to include non-road and on-road, spark-ignition 2-cycle and 4-cycle engines, non-spark ignition engines, and handheld (HH) and non-handheld (NHH) engines .

[0024] In FIG. IA, a ceramic nanofiber and/or ceramic microfiber matrix 2, is formed on a permeable or non- permeable layer support structure 4, of ceramic, metallic, or ceramic/ metallic composite material whereas, in FIG. IB, a permeable ceramic nanofiber/microfiber matrix 6, is formed.

[0025] As shown in FIG. 2A and FIG. 2B, two different application strategies can be employed. The direction of gas flow emissions is indicated by the arrow 7 in the support structure of FIG. 2A. In the first level 8 of the support structure of FIG. 2A, a ceramic nanofiber/microfiber composite matrix is employed for the removal of particulate materials (PM) and hydrocarbon (HC) removal/oxidation and in the second level 10 of support structure of FIG. 2A a single layer of catalyzed ceramic nanofiber/microfiber composite matrix with multiple catalysts is employed to enhance oxidation of HC, reduction of NO_x and SO_x, and destruction of CO. As shown in the structure of FIG. 2B instead of the single second level 10, multiple individual catalyst layers, 12.14. and 16, are employed as a substitute for the single layer in the second level 10 to enhance oxidation of HC, reduction of NO_x and SO_x, and destruction of CO.

[0026] FIG. 3A and FIG. 3B illustrate two configurations for immobilizing ceramic nanofibers and ceramic microfibers 18, alone or in combination, on a non-permeable support structure 20 or a permeable support structure 22, each constructed from ceramic, metallic, or a combination of ceramic/metallic composite materials. As shown by the arrows 19, Gas emissions flow over the non-permeable coated support structure 20, while as shown by the arrows 21, gas emissions can flow through the permeable support structure 22. Ceramic nanofibers, ceramic microfibers, and * various combinations of ceramic nanofibers with ceramic microfibers in a composite matrix can be applied either directly to the support structure or by the use of an intermediate layer to enhance bonding between the support structure and the fibrous materials. Gas emissions flow through the fiber matrix and, in the case of a permeable support structure, through the fiber support results in the removal of PM, HC removal/oxidation, reduction of NO_x and SO_x, and destruction of CO. [0027] Inert structures are desirably used that promote and allow the flow of gases and particulates through a series of channels or voids in which ceramic nanofibers, ceramic microfibers, or a combination of ceramic nanofibers/microfibers with or without embedded catalyst materials, or catalyst coatings can be immobilized. Specific examples of inert, rigid structures comprised of ceramic, metallic, or ceramic/metallic composite materials include multi-channel support structures in single or multiple layers (corrugated configurations) as shown in FIG. 4A with exhaust gas flow direction indicated by the arrows 25, and traditional "honeycomb" monolithic configurations structures of various sizes as illustrated in FIG. 4B with the direction of exhaust gas flow indicated by the arrows 29.

[0028] A specific example of a random oriented fibrous support structure 24 utilizing ceramic microfibers 26 as a ceramic nanofiber 28 support matrix is illustrated in FIG.5.

[0029] It should be apparent that many different types of catalyst support structures can be used to immobilize ceramic nanofibers and/or ceramic microfibers with or without catalyst materials to treat internal combustion exhaust sources promoting chemical reactions and particulate removal/destruction. FIGS 1, 2, 3, 4, and 5 of the present application relate to various methods of utilizing ceramic nanofiber/microfiber structures and coatings, and illustrate support configurations for immobilizing ceramic fibrous materials. [0030] Inert support structures can be made out of various materials. Ceramic materials include all metal oxide structures, desirably from aluminum oxide (Al₂O₃) , ceria oxide (CeO₂) , ceria/zirconia oxide (Ce/ZrO₂) , tin oxide (SnO₂) , titanium oxide (TiO₂) , and zinc oxide (ZnO₂) , and preferably from high-temperature, thermally stable structural polymorphs of aluminum oxide, ceria oxide, zirconia oxide, and mixed ceria/zirconia oxide materials. Metallic support structures can include various grades of stainless steel or carbon steel. Coatings on the stainless steel or carbon steel support structures can include, but are not limited to, ceramic and or/intermediate conditioning layers.

[0031] Various ceramic materials can be used to produce ceramic nanofibers and ceramic microfibers as well as a broad range of possible catalytic materials for use in accordance with this invention. Preferred ceramic nanofibers and ceramic microfibers have a metal oxide or mixed metal oxide composition, desirably aluminum oxide (Al₂O₃) , ceria oxide (CeO₂) , ceria/zirconia oxide (Ce/ZrO₂) , tin oxide (SnO₂) , titanium oxide (TiO₂) , and zinc oxide (ZnO₂) materials, and preferably high-temperature, thermally stable structural polymorphs of aluminum oxide, ceria oxide, zirconia oxide, and mixed ceria/zirconia oxide materials. Catalyst materials include metals from the noble group and also known metals with catalytic properties. Specific examples of catalyst materials incorporated include platinum (Pt), palladium (Pd), rhodium (Rh), and other noble metals.

[0032] The amount of ceramic nanofibers and ceramic microfibers coated and/or attached to a ceramic, metallic, or ceramic/metallic composite support structure will vary depending on the application and the anticipated conditions during use. The average surface coating will utilize 0.1 to 150 g/m², desirably from 0.5 to 60 g/m², and preferably from 1 to 30 g/m² of the mass of ceramic nanofibers, ceramic microfibers, or a combination of ceramic nanofibers/microfibers with or without catalyst particles, or catalyst coating per surface area of support structure where fibers are applied.

[0033] The ceramic nanofibers described throughout this application can be produced by any suitable method, however, electrospinning methods have been found to be preferable. Examples of catalyzed ceramic nanofibers utilizing aluminum oxide (AI₂O₃) as a ceramic immobilizing structure for various single metal catalyst materials include, palladium (Pd); platinum (Pt), rhodium (Rh), and cerium (Ce) . Each ceramic nanofiber contains nano-size particles of elemental catalysts within and on the surface of each nanofiber where catalyst particles are partially embedded within the nanofiber, therein immobilizing the catalyst particles. The nanofibers have an average diameter of 1 to 500 nm, desirably from about 5 to about 25 to about 250 nanometers, and preferably from about 50 to 100 nanometers while the catalyst particles have an average size of 0.1 to 1,000 nanometers, desirably from about 0.5 to 20, and preferably from about 1 to 15 nanometers

[0034] TABLE 1 relates to a list of ceramic materials that can be utilized as nanofibers and microfibers within composite materials and a list of the possible catalyst/reactive materials integrated into ceramic nanofibers/microfiber composites supported by permeable or non-permeable rigid or fibrous structures.

TABLE 1

Ceramic Nanofiber and/or Catalyst/Reactive

Microfiber Materials Materials

Al₂O₃-B₂O₂ Ag

NiFe₂O₄ Au

Al₂O₃ Pt

Co₃O₄ Pd

MgTiO₃ Rh

NiTiO₃ Ru

ZrO₂ I r

Mn₂O₃-Mn₃O₄ Os

SnO₂ Ti

CeO₂ V

SiO₂ Cr

ZnO Mo

CrO₃ Mn

WO₃ Fe

ZnO₂ Co

CeO₂-ZrO₂ Ni

InO₃ Zn

Er

Ga

Ge

[0035] Ceramic nanofiber materials listed in TABLE 1 can be integrated into various porous composite mediums with varying amounts of nanfibers to dictate the surface area of catalyst or catalysts within the medium, bulk porosity, and particulate removal efficiencies. Composite mediums generally will be made with a combination of ceramic nanfibers and microfibers into a surface coating on a rigid inert support structure or into a woven or non-woven mat and the like to provide suitable reinforcement and support of the composite medium. The composite mediums can either be supported internally or externally by the use of ceramic or metal screens, meshes, perforated tubes and plates, and the like. Additional microfiber materials may include metal fibers or glass fibers. Ceramic nanofibers and catalyzed ceramic nanofibers may either be at the top or bottom regions of the composite medium, or randomly dispersed throughout.

[0036] The present invention employs the use of a self- contained catalytic device that incorporates ceramic nanofibers and ceramic microfibers alone or in combination, with or without catalyst materials, support structures, inlet/outlet gas ports, passive secondary air injection system, and external housing used either before of after existing emission control components for internal combustion engine exhaust sources. The ceramic nanofiber/microfiber materials can be immobilized within the self-contained device by a variety of methods including the use of ceramic and non-ceramic materials, fibrous structures, amorphous ceramic structures, extruded materials, formed ceramic support structures, metallic forms, or combinations of ceramic and metallic materials. These ceramic and metallic composite materials act as filter and catalyst mediums for the removal and destruction of hydrocarbons (HC), particulate material (PM), nitrogen oxides (NO_x) , sulfur oxides (SO_x) , and carbon monoxide (CO) . A secondary air injection system is optional and may be used to enhance and improve oxidative reactions such as HC and CO destruction/conversion reactions. Both direct and passive air, oxygen, and other oxidant compounds injection technologies can be used.

[0037] The emission control device and composite materials of the present invention are desirably made by incorporating ceramic nanofiber/microfiber materials along with catalyzed ceramic nanofiber/microfiber materials into either a self-contained, stand alone unit; incorporated into an emission control/muffler combination; or used as a media for advanced emission control systems.

[0038] Ceramic nanofibers, ceramic microfibers, a combination of ceramic nanofibers/microfibers, with or without catalyst particles, or catalyst coatings can be arranged to target specific reactants or particulate materials by using single or multiple fiber layers, with separate, distinct catalyst and ceramic materials within each layer, and/or with multiple catalyst and ceramic materials with each layer as illustrated in FIG. 2. These fibrous layers can be applied to rigid or fibrous, permeable or non-permeable support structures. Non- catalyzed ceramic nanofiber/microfiber composite materials are generally placed upstream of catalyzed ceramic nanofiber/microfiber composite materials to remove, or capture, or destroy particulate material (PM) and hydrocarbon materials (HC) to limit catalyst deactivation due to surface coverage and catalyst blockage by particulates, coalescence, and adsorption of organic and inorganic materials, and poisoning by undesirable gaseous components. In certain circumstances the ceramic nanofiber without embedded catalyst materials may serve as the primary catalyst/reactive material. Catalyzed ceramic nanofiber/microfiber composite materials are generally placed downstream of non-catalyzed ceramic nanofiber/microfiber composite materials to facilitate the destruction/conversion of gaseous constituents within the exhaust stream including but not limited to oxides of nitrogen and sulfur (NO_x and SO_x) , hydrocarbon materials

(HC) , and carbon monoxide (CO) . [0039] Multiple layers, or support structures with either mixed or single component catalyst materials can be used within a stand-alone, self-contained device, or integrated into an emission control/muffler combination, or provided as a supported, or unsupported media for emission control systems. Multiple catalyst materials may contain 2 or more catalyst materials.

[0040] One or more catalyst materials can be incorporated into ceramic nanfibers resulting in either a multi-functional medium that can be integrated into processes where different reactions can occur simultaneously or in a single medium that can facilitate single reactions. Multi-functional and single-functional composite mediums can be placed at different locations within pollution control systems to separate desired reactions dependent on temperature, contaminant concentration, reaction rates, etc.

[0041] Ceramic composite materials described within the present invention are desirably included into a self- contained device, or into catalyst/muffler combination, or immobilized onto a rigid support structure by either sintering the ceramic composite medium to a support media or vacuum molding onto an external support structure. The ceramic nanfober/microfiber can be attached to an external support structure or can be placed within a larger, advanced emission control device. FIG. 6 shows one example of a self-contained catalyst delivery system using perforated tube structures 35 coated with ceramic nanofiber/microfiber materials with and without catalyst materials. The catalyst delivery system uses ceramic nanofiber/microfiber composite material for PM and HC removal/oxidation and a mixed catalyzed ceramic nanofiber/microfiber composite for oxidation of HC, reduction of NO_x and SO_x, and destruction of CO. The delivery system includes a gas inlet 50 and a gas outlet 51, two end-plates 30 with appropriate connections, an outer containment shell 32, surrounded by insulation 33, with an internal spacer 34 used for proper internal component alignment 34, and an internal support structure for the ceramic nanofiber/microfiber media 35 and catalyzed ceramic nanofiber/microfiber composite media 36 and integrating the option of passive secondary air injection system or systems before or within the catalytic chamber 37.

[0042] An additional embodiment of the present invention is illustrated in FIG.7 which shows a Front view A and a Rear view B of a self-contained device with an interchangeable ceramic nanofiber/microfiber cartridge, or multiple interchangeable cartridges that can be directly mounted to an existing exhaust muffler or emission control device. This delivery system includes two separable plates 41 and 42 with appropriate mounting connections with an exhaust inlet 43 and a treated exhaust exit 44, with internal spacing and compartments where preformed cartridges containing ceramic nanofiber/microfiber composite materials 45 with, or without, catalyst materials can be placed.

[0043] Catalyst loading ratios will vary depending on the application and operating conditions with mass loadings of 1 to 150 g/ft³, desirably 5 to 50 g/ft³, and preferably from about 5 to 35 g/ft³ of composite ceramic nanofiber/microfiber material. Although not limited in scope, generally the type of catalyst combinations incorporated into the final composite materials include platinum (Pt), palladium (Pd), and rhodium (Rh) either singly or in the following combinations; Pd: Pt, Pd: Rh, Pt: Rh, or Pd: Pt: Rh ( tri-metallic platinum group metal, PGM) . The ratios of platinum, palladium, and rhodium in the various described combinations above are dependent on the specific application environment and can be controlled and tailored during the formulation stage of composite media production.

[0044] Secondary air injection systems using passive injection technologies may be used to enhance, promote HC and CO destruction/conversion reactions within the entire catalytic chamber or within specific regions within a catalytic emission control device. Passive secondary air injection systems may include but are not limited to Venturis, ejectors, pulse-air injection, check valves, etc., and the like.

[0045] The invention described herein, namely the use of immobilized ceramic fibers such as ceramic nanofibers and/or ceramic microfibers, with and without embedded metal catalyst particles, or catalytic coatings, provides a significant technological advance to catalytic systems for the treatment of gaseous and particulate components from internal combustion engine exhaust to destroy nitrogen oxides (NO_x) , sulfur oxides (So_x) and carbon monoxide (CO) gaseous components and the capture and oxidation of soot particles and other hydrocarbon (HC) constituents, methane and non-methane hydrocarbon materials [0046] Multiple types of ceramic fibers, either catalyzed or non-catalyzed can be integrated into a medium to react with specific gaseous components. Catalyzed or non-catalyzed fibers can be applied in multiple, distinct layers with different compositions to sequentially react with specific gaseous components. Ceramic nanofibers provide a significant increase in fiber surface area compared to other fiber types therein increasing the surface area to volume ratios compared to other mediums. The use of ceramic nanofibers also increases the thermal stability of attached and/or embedded catalyst particles within the ceramic nanofiber matrix since small catalyst particles present on and/or within a ceramic nanofiber matrix do not readily coalesce (merge) into larger catalyst particles at high application temperatures catalytic performance at high temperatures is maintained. With the enhanced thermal stability and the use of small catalyst nanoparticles significant cost savings as compared to existing technologies are realized. The use of ceramic fibers (nano- and micro-) within a catalytic medium and/or conduit immobilized by various support structures, both fibrous and rigid, also enhance fluid flow to the catalyst surfaces therein increasing overall catalyst use efficiencies.

Claims

WHAT IS CLAIMED IS :

1. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines, comprising immobilized ceramic fibers:

2. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers includes ceramic nanofibers.

3. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic microfibers.

4. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers includes catalyst material contained therewith.

5. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers includes both ceramic microfibers and ceramic nanofibers.

6. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers includes both ceramic microfibers with catalytic material contained therewith and ceramic nanofibers.

7. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers includes both ceramic nanofibers with catalytic material contained therewith and ceramic microfibers.

8. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers are self supported.

9. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include a metallic support.

10. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers are formed in a single composite layer.

11. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers are formed in a multitude of layers with the various layers provided to primarily treat different contaminants .

12. A device for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1 further comprising, a plurality of ceramic nanofibers with an average fiber diameter from about I to 500 nanometers.

13. A device for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim I further comprising, a plurality of ceramic nanofibers with an average fiber diameter from about I to 250 nanometers.

14. A device for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim I further comprising, a plurality of ceramic nanofibers with an average fiber diameter from about 50 to 100 nanometers.

15. A device for use in the treatment of gaseous exhaust emissions from internal combustion engines comprising, a plurality of ceramic nanofibers with dispersed catalyst nanoparticles, said catalyst nanoparticles having a surface area coverage from about 1% to 90%, . depending on the surface area of the nanofiber.

16. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include a metallic support made from noble and non-noble metals.

17. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers made from aluminum oxide.

18. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers made from high-temperature, thermally stable structural polymorphs of aluminum oxide.

19. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim I, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers made from ceria oxide.

20. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim I, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers made from ceriazirconia oxide.

21. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers comprising tin oxide.

22. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers comprising titanium oxide.

23. A fibrous structure for use in the treatment of gaseous exhaust emissions from internal combustion engines as defined in claim 1, wherein said immobilized ceramic fibers include ceramic nanofibers and ceramic microfibers comprising zinc oxide.