Apparatus For Removing Mixed Nitrogen Oxides, Carbon Monoxide, Hydrocarbons And Diesel Particulate Matter From Diesel Engine Exhaust Streams At Temperatures At Or Below 280 Degrees C

Abstract

Disclosed is a catalytic unit that removes contaminates and particulates, including nitrogen oxides and soot, from diesel engine emissions without the use of chemical agents. The disclosed apparatus comprises a flow through device in fluid communication with a reduction unit, which is in fluid communication with a diesel particulate filter. The flow through device is coated with hematite and bixbyite in a ratio ranging from 1:1 to 9:1. The reduction unit is a catalytic substrate comprising one or more transition metals supported on a molecular sieve coated with an oxide catalyst. The diesel particulate filter has an oxide coating and a noble metal coating. The flow through device converts nitric oxide into nitrogen dioxide. The reduction unit converts most of the nitrogen dioxide into nitrogen, water, carbon monoxide and carbon dioxide. The diesel particulate filter traps remaining soot and coverts it and the carbon monoxide into carbon dioxide.

Description

[0001] This disclosure relates to the removal of contaminants and particulates from exhaust gases generated by diesel engines. More particularly, this disclosure relates to a passively-regenerated diesel filter for the removal of several materials from diesel exhaust gas at low temperatures, including carbon monoxide, hydrocarbons, diesel particulate matter and various nitrogen oxides, including nitrous oxide, nitric oxide, nitrogen sesquioxide and nitrogen dioxide. This invention employs in situ catalytic units in place of technology using ammonia or ammonia derived from urea and does not require the application of liquid hydrocarbons or gaseous hydrocarbons.

BACKGROUND OF THE INVENTION

[0002] The combustion of fossil fuels, such as gasoline or diesel fuel, leads to the formation of harmful substances. Diesel engines, in particular, produce four major emissions: nitrogen oxides (NOx), diesel particulate matter (material suspended in the air in the form of minute solid particles or liquid droplets), hydrocarbons and carbon monoxide. Nitrogen oxides react with water to form nitric acid (HNO.sub.3), which is a major contributor to acid rain. Nitrogen oxides can also detrimentally react with ozone. The United States and other jurisdictions have increasingly required NO.sub.X emission reductions from stationary and mobile sources. Further, these jurisdictions also regulate the emission of hydrocarbons.

[0003] The exhaust emitted from internal combustion engines needs to be treated prior to being emitted in order to meet these increasingly stringent exhaust emission standards. The removal of various unwanted contaminants from diesel exhaust gas has required increasingly complex technology. In the context of gasoline engines, catalytic converters have become ubiquitous in the industry to attempt to remove harmful materials from the exhaust. For example, three-way catalysts have been developed to reduce NO.sub.x in the rich-burn exhaust found in automobiles. These catalysts, however, are not as effective in the lean-burn conditions found in diesel vehicles. Further, abatement devices for diesel engines present different problems than those for gasoline engines because the formation of complex nitrogen gases, carbon monoxide, raw hydrocarbons and soot is common in the operation of a diesel engine.

[0004] Diesel particulate matter includes soot, which consists of finely divided carbon and hydrocarbons. Soot is particularly difficult to remove from diesel exhaust. A device known as a diesel particulate filter (DPF) is one way to remove soot from a diesel engine. These filters are made of a porous ceramic or metal substrate that allows the exhaust gases to pass through the filter but traps the small carbon particles. These filters, however, often become clogged with the soot generated by the engine, causing a potentially-harmful backpressure increase in the engine. Higher backpressure creates a fuel economy penalty. High backpressure can also cause an engine to stall or result in engine damage.

[0005] So-called active regeneration devices exist that use heat or chemicals (or a combination of both) to remove soot from the filter. Some of these devices operate by spraying raw diesel fuel into the filter chamber and igniting the fuel and soot in situ. This process, along with the presence of oxygen, ignites the soot at a sufficiently high temperature (600.degree. C.) to convert it into either carbon monoxide or carbon dioxide. This process temporarily clears the filter. These devices require a backpressure monitoring apparatus, a fuel injection system and instrumentation to control the monitoring of the filter and the cleaning system.

[0006] Some applications use off-board regeneration. That process, however, requires operator intervention because the device must be plugged into a wall/floor mounted regeneration station, or the filter must be removed from the machine and placed in the regeneration station. Off-board regeneration is generally not used in connection with on-road vehicles, such as diesel vehicles, except in situations where the vehicles are parked in a central depot when not in use.

[0007] Passive regeneration can also be used to remove soot from the filter. Passive regeneration occurs when the soot in the diesel particulate filter spontaneously combusts during the engine's normal work cycle. This combustion only occurs when the exhaust temperatures are sufficiently hot, requiring high temperatures (as high as 650.degree. C.). Certain techniques have been developed that can lower the temperature required for passive regeneration, including coating the surface of the substrate used in the filter with noble metal catalysts such as platinum. This technique, however, has the undesirable effect of increasing the emission of nitrogen dioxide (NO.sub.2), a harmful gas. Further, these passive regeneration devices also use large amounts of platinum or other noble materials, driving up the cost.

[0008] The NO.sub.x series, including nitrous oxide (N.sub.2O), nitric oxide (NO), nitrogen sesquioxide (N.sub.2O.sub.3) and nitrogen dioxide (NO.sub.2), is also difficult to remove from diesel exhaust. New technologies have been created to remove NO.sub.X from exhaust streams. As noted above, three-way catalysts have been developed to reduce NO.sub.X in the rich-burn exhaust found in automobiles. These catalysts, however, are not as effective in lean-burn conditions found in diesel vehicles. In the oxygen-rich environment of diesel exhaust, chemically reducing NOx to molecular nitrogen is difficult. This conversion of NO.sub.x in the exhaust stream requires a reductant (HC, CO or H.sub.2) and, under typical engine operating conditions, sufficient quantities of reductant are not present to facilitate the conversion of NO.sub.x to nitrogen.

[0009] For stationary sources, ammonia may be used to reduce NO.sub.X. For example, urea ((NH.sub.2).sub.2CO.sub.2) is used to convert NOx gases to N.sub.2 and H.sub.2O. This method of reducing NO.sub.X is not preferred for mobile sources such as diesel vehicles because of the toxic nature of ammonia and the storage requirements. Further, the use of ammonia as a method of reducing NO.sub.X is hampered by the lack of availability. Unlike with regular gasoline or diesel fuel, there are few readily-available commercial sources of refueling and disposal for ammonia-based reductants. Further, these reactions occur at relatively high temperatures and the materials are difficult to use because of their corrosive nature and relatively high freezing point.

[0010] There are also systems which use diesel fuel which is dosed onto the catalyst body in order to accomplish the selective reduction of the NOx gases. As noted above, controlling NOx emissions from a diesel engine is difficult because diesel engines are designed to run lean. Some lean NOx catalyst systems inject diesel fuel or another reductant into the exhaust upstream of the catalyst. The fuel or other hydrocarbon reductant acts as a reducing agent for the catalytic conversion of NOx to N.sub.2. Typically, in these systems, a computer monitors one or more sensors that measure backpressure and/or temperature, and the computer makes decisions on when to activate the regeneration cycle. The additional fuel is generally supplied by a metering pump. Running the cycle too often while keeping the backpressure in the exhaust system low uses extra fuel. Not running the regeneration cycle soon enough increases the risk of engine damage and/or uncontrolled regeneration (from an excess of accumulated soot) and possible filter failure. Therefore, these methods are complicated and significantly impact fuel efficiency.

[0011] Selective catalytic reduction (SCR) of NO.sub.X with hydrocarbons has been used under lean-burn conditions such as those found in diesel engines. Materials found to be catalytically active for SCR include metal-exchanged zeolites, such as Cu-ZSM-5, Co-ZSM-5 and Fe-ZSM-5. These zeolites are very active for SCR using C.sub.3 hydrocarbons. These materials, however, lose much of their activity when water is added to the exhaust stream, which is common due to the presence of water in exhaust. Although the exact cause of the loss of activity due to the introduction of water is unknown, delumination of the zeolite framework may occur, reducing the number of active sites, or the metal sites may over-oxidize and lose their activity.

[0012] Marshall, et al., U.S. Pat. No. 7,220,692 (the "'692 Patent"), discloses a zeolite-based catalyst that demonstrates increased stability in water. Disclosed are bifunctional catalysts that combine active-metal exchanged molecular sieves with a separate metal oxide stabilizing phase forming an oxide coating thereon. The material is in essence a two-phased catalyst comprising one or more transition metals supported on a molecular sieve and one or more stabilizing oxides coating the sieve material. The preferred embodiment of the material is a catalyst composed of a zeolite-supported copper metal impregnated with a ceria stabilizing oxide. The catalyst, however, can be comprised of any number of zeolite materials including zeolite Y, zeolite Beta, mordenite, ferrierite, ZSM-5 or ZSM-12.

[0013] The use of the material disclosed in the '692 Patent, however, requires the use of organic reductants, primarily diesel fuel. Therefore, the use of that zeolite-based catalyst requires the use of additional fuel, reducing the fuel efficiency rating of the vehicle in which it is used and creating additional expense.

SUMMARY OF THE INVENTION

[0014] The present invention relates to a passively-regenerated diesel filter for the removal of several materials from diesel exhaust gas at low temperatures, including carbon monoxide, hydrocarbons, diesel particulate matter and various nitrogen oxides, including nitrous oxide, nitric oxide, nitrogen sesquioxide and nitrogen dioxide. It is the object of this invention to provide an in situ catalytic unit that does not require the use of chemical agents such as ammonia or additional fuel as a reducing agent. It is a further object of this invention to allow the removal of contaminants and particulates from diesel exhaust gas at temperatures typical in diesel engines (at or below 280.degree. C.).

[0015] The disclosed invention is an apparatus for removing contaminants and particulates, including nitrogen oxides and soot, from diesel engine emissions. The preferred embodiment of this apparatus comprises a flow through device in fluid communication with a reduction unit, which is in turn in fluid communication with a diesel particular filter. The flow through device is preferably coated with a catalyst comprising hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3) where the ratio of hematite to bixbyite ranges from 1:1 to 9:1. The reduction unit preferably comprises a catalytic substrate coated with a catalyst, with the substrate comprising one or more transition metals supported on a molecular sieve and the catalyst comprising one or more stabilizing oxides coating the molecular sieve. The diesel particulate filter is coated with a first coating comprising tin oxide, aluminum oxide and zirconium oxide and a second coating comprising platinum, palladium, silver or gold.

[0016] The flow through device and reduction unit may be used with other filters. Another embodiment of the invention is an apparatus for removing contaminants and particulates, including nitrogen oxides and soot, from diesel engine emissions, comprising: a flow through device coated with a catalyst comprising hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3), where the ratio of hematite to bixbyite ranges from 1:1 to 9:1. The flow through device is in fluid communication with a reduction unit comprising a catalytic substrate coated with a catalyst, with the substrate comprising one or more transition metals supported on a molecular sieve and the catalyst comprising one or more stabilizing oxides coating the molecular sieve.

[0017] In the various embodiments of the invention, the second coating for the diesel particulate filter may be comprised of platinum. Further, the molecular sieve is preferably comprised of zeolite. The transition metal coating for the catalytic substrate may include one or more of Cu, Co, Fe, Ag or Mo or may be comprised of copper or iron. The stabilizing oxide may preferably be cerium oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The FIGURE depicts a preferred embodiment of the claimed apparatus. Exhaust is generated by the engine 1 and flows into a sealed container 2 housing the catalytic elements. The exhaust gas first passes through the flow through device 3, through the reduction unit 4, and then into the diesel particulate filter 5. The treated exhaust gas is then emitted from the sealed contained through an opening 6.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to an apparatus that removes harmful pollutants from a diesel engine exhaust system at relatively low temperatures (at or below 280.degree. C.). The invention prevents the plugging of diesel particulate filters while converting carbon monoxide (CO) to carbon dioxide (CO.sub.2), nitrogen oxides (NOx) to nitrogen (N.sub.2) and passively regenerating the soot trap portion of the device. Specific catalysts in the flow through device alter the composition of the exhaust gases so that the gases react with the carbon and hydrocarbons formed in the diesel engine during combustion. The reaction of the carbon and hydrocarbons in the reduction unit forms carbon monoxide. After further reaction, gaseous carbon dioxide forms, which no longer can plug the filter.

[0020] The disclosed invention is comprised of three different elements contained in a single catalytic converter. The first element converts nitric oxide (NO) into nitrogen dioxide (NO.sub.2). The second element is an area where selective catalytic reduction (SCR) occurs, converting most of the nitrogen oxide (NOx) into nitrogen (N.sub.2), water (H.sub.2O), carbon monoxide (CO), and carbon dioxide (CO.sub.2). The third element traps any remaining soot and converts it to CO.sub.2 while simultaneously converting CO into CO.sub.2.

[0021] The first element consists a device with a ceramic coating comprised of hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3). The device oxidizes NO to NO.sub.2, increasing the amount of NO.sub.2 by approximately 30 to 50%. The increased amount of NO.sub.2 flowing into the diesel particulate filter allows more effective oxidation of the soot. The coating for the substrate comprises hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3), with a ratio of hematite to bixbyite ranging from 1:1 to 9:1.

[0022] The second element has a reduction unit comprising a catalytic substrate coated with a specially prepared zeolite-based catalyst. The nitrogen dioxide-enhanced exhaust flows through this unit and is converted into nitrogen, water, carbon monoxide and carbon dioxide. The remaining NO.sub.x is partially reduced to N.sub.2 and the soot is converted to water vapor, CO and CO.sub.2. The coating is in essence a two-phased catalyst comprising one or more transition metals supported on a molecular sieve and one or more stabilizing oxides coating the sieve material. A preferred embodiment of this coating is a catalyst composed of a zeolite-supported copper metal impregnated with a ceria stabilizing oxide. Another preferred embodiment of this coating is a catalyst composed of a zeolite-supported iron metal impregnated with a stabilizing oxide.

[0023] The zeolite coating material is blended with a tin oxide catalyst. This material is described in Summers et al., U.S. Pat. No. 7,056,856 (the "'856 Patent), which describes a tin oxide catalyst employing precious metals. The material is a three-way tin-oxide based catalytic material that is stable at exhaust gas temperatures of internal combustion engines when the tin oxide lattice includes hafnium and/or any of several rare earth oxide components in the lanthanide series, such as oxides of La, Pr and Nd. The rare earth oxides replace or supplement the transition metal oxide promoters in prior art tin oxide catalysts. This replacement or supplementation provides a high degree of thermal stability as measured by the Brunauer/Emmett/Teller (BET) surface area in the range of temperatures required for automotive uses.

[0024] The third element is a diesel particulate filter (DPF) coated with a ceramic composition comprising, among other things, tin oxide, aluminum oxide and zirconium oxide. This element acts to trap any remaining soot and convert the remaining by-products to N.sub.2, CO.sub.2 and water vapor. After the filter is coated with the ceramic composition, a coating of platinum is precipitated onto the filter. Again, this process occurs at a temperature lower than 280.degree. C. The lower temperature removal of soot is beneficial because it occurs at normal exhaust temperatures. Further, the increased NO.sub.2 generation from the preceding elements within the device decreases the amount of platinum required in the filter, lowering the cost of the soot removal apparatus.

[0025] A preferred embodiment of the apparatus includes a flow through device in fluid communication with an reduction unit, which is in turn in fluid communication with a catalyzed diesel particulate filter. Preferably, the flow through device, reduction unit and the diesel particulate filter will be placed in a sealed container, such as one made of stainless steel or other suitable material, to prevent the escape of gases. The diesel exhaust is received by the flow through device and passes through the device and the reduction unit, and into the filter before being emitted into the atmosphere.

[0026] The flow through device may be made from cordierite, stainless steel, or a primarily nonferrous metal. Alternatively, the flow through device may be made from a ceramic material or any other material common to use in the art. The substrate is coated with an oxide formulation of hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3), wherein the ratio of hematite to bixbyite ranges from 1:1 to 1:9. The optimum ratio of hematite to bixbyite for low temperature removal of soot is about 1:7, where the NO.sub.2 formation increases by up to 50% at temperatures lower than 100.degree. C. Ratios from 4:1 to 9:1 also increase NO.sub.2 formation at temperatures lower than 100.degree. C. This material is disclosed in a pending patent application which is incorporated by reference.

[0027] In one preferred embodiment, the substrate is coated using solution made from a ferric salt and a manganese salt prepared by the coprecipitation method. The substrate is coated immediately after the ferric salt and manganese salt are combined. The coated substrate is dried and calcinated at 500.degree. C. for two hours. During the drying, the coating undergoes a shrinkage process which causes micro-cracks to form in the surface, increasing the surface area of the coating. The heating, among other things, stabilizes the oxidation state of the composition and bonds the individual grains to the surface of the substrate. Crystallographic changes also occur during the heating process, where the small precipitates become crystals, further increasing the surface area. Thereafter, the material goes through a shrinkage process during the heating due to water loss and sintering. It is understood that the coating may be prepared in any other manner that creates the correct proportion of hematite and bixbyite and results in a thin layer of the coating covering the surface of the substrate.

[0028] The second element of the device is a reduction unit in fluid communication with the flow through device. In the preferred embodiment of the invention, this element converts between 20% and 99% of the NO.sub.x into N.sub.2. The reduction unit is made by coating a suitable substrate (consisting of ceramic material, metal or porous metal foam) with a cerium-copper zeolite material which has been specially prepared for coating. Marshall, et al., U.S. Pat. No. 7,220,692 (the "'692 Patent"), discloses a zeolite-based catalyst that combines active-metal exchanged molecular sieves with a separate metal oxide stabilizing phase forming an oxide coating thereon. The catalyst is in essence a two-phased catalyst comprising one or more transition metals supported on a molecular sieve and one or more stabilizing oxides coating the sieve material. Preferably, the catalyst is composed of a zeolite-supported copper metal impregnated with a ceria stabilizing oxide. The catalyst, however, can be comprised of any number of zeolite materials including zeolite Y, zeolite Beta, mordenite, ferrierite, ZSM-5 or ZSM-12. In addition, the catalyst may be composed of a zeolite-supported iron metal impregnated with a stabilizing oxide.

[0029] Any transition metal may be supported by the molecular sieve, including the commonly-used transition metals copper, cobalt, iron, silver, molybdenum, vanadium and combinations thereof. The supporting oxides that coat the molecular sieve material can be any one or more of the rare earth oxides such as cerium oxide and transition metal oxides, such as zirconium oxide, molybdenum oxide, vanadium oxide and niobium oxide. A preferred embodiment consists of cerium oxide alone or in combination with one or more of the other rare earth oxides. All of the preferred oxides are added in the form of metal oxide sols.

[0030] The diesel particulate filter, which may be of any type available for purchase, may be coated with a ceramic wash coat comprised of tin oxide, aluminum oxide and zirconium oxide. In one embodiment, the molar ratio of the tin oxide will be approximately 0.53, the molar ratio of the aluminum oxide will be approximately 0.14 and the molar ratio of the zirconium oxide will be approximately 0.24. The coating may also additionally be composed of silicon oxide and lanthanum oxide. The oxide of any rare earth element of Group IIIA of the periodic table, including cerium, praseodymium, neodymium, promethium, samarium, europium, thulium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium and lutetium, may be substituted for the lanthanum oxide. In another embodiment, the molar ratio of the tin oxide is approximately 0.53, the molar ratio of the aluminum oxide is approximately 0.14, the molar ratio of the zirconium oxide is approximately 0.24, the molar ratio of the silicon oxide is approximately 0.04 and the molar ratio of the rare earth oxide is approximately 0.05.

[0031] Preferably, the aluminum oxide is gamma alumina coated with silica. The remaining oxides may be added as salts and hydroxides which are mixed into the alumina-silica mixture to make a fine precipitate. Thereafter, the precipitate may be washed and dried, and thereafter ground to an apparent particle size of approximately 0.1 and 0.9 micrometers prior to coating. The final coating, after application and drying, will have an average particle size of 20 to 40 nanometers. A coating of platinum, gold, silver or palladium is placed on the filter after the ceramic coating. Preferably, platinum will be used and may be applied as a nitrate or a tera-amine platinum nitrate. The platinum may be applied through various methods, including submersion, waterfall coating, spraying or any other recognized coating method. The preferred result of the coating, regardless of the method, is a uniform nano-sized dispersion of the platinum metal over the ceramic coating. Any fairly uniform dispersion of the platinum within commercially acceptable tolerances may be used, however. The percentage of platinum may vary with the application and the system design, ranging from approximately 0.5 grams per liter to 5.0 grams per liter. The filter is then heat treated at 500.degree. C.

[0032] The invention removes soot from the diesel particulate filter at low temperatures (at or less than 280.degree. C.). In one of the preferred embodiments, the Group IIIA elements (including lanthanum) oxidize CO and HC as well as carbon at low temperatures. An oxygen removed from the NO.sub.2 combines with the carbon in the filter to form CO and CO.sub.2. The catalysts in the ceramic coating act as an environment to store the allotrope of oxygen so that the reaction may occur at low temperatures. The flow through device facilitates the operation of the filter because it increases the NO.sub.2 flowing into the diesel particulate filter. Other benefits of the disclosed apparatus exist or may be discovered.

[0033] Ideally, the apparatus would use the coated flow through device, the reduction unit and the coated diesel particulate filter. The flow through device and reduction unit, however, may be used with other filters and may have applications other than those stated.

Claims

1. An apparatus for removing contaminants and particulates, including nitrogen oxides and soot, from diesel engine emissions, comprising: a flow through device coated with a first catalyst comprising hematite (Fe.sub.2O.sub.3) and bixbyite ((Mm.sub.1.5,Fe.sub.0.5)O.sub.3) wherein the ratio of hematite to bixbyite ranges from 1:1 to 9:1; wherein said flow through device is in fluid communication with an reduction unit comprising a catalytic substrate coated with a second catalyst, said substrate comprising one or more transition metals supported on a molecular sieve and said second catalyst comprising one or more stabilizing oxides coating the molecular sieve; wherein said reduction unit is in fluid communication with a diesel particulate filter coated with a first coating comprising tin oxide, aluminum oxide and zirconium oxide and a second coating comprising gold, silver, palladium or platinum.

2. An apparatus according to claim 1 wherein the second coating comprises platinum.

3. An apparatus according to claim 2 wherein the molecular sieve is zeolite.

4. An apparatus according to claim 2 wherein in the molecular sieve is zeolite and the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

5. An apparatus according to claim 2 wherein the molecular sieve is zeolite and the transition metal is Cu.

6. An apparatus according to claim 2 wherein the molecular sieve is zeolite and the transition metal is Fe.

7. An apparatus according to claim 2 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

8. An apparatus according to claim 2 wherein the transition metal is Cu.

9. An apparatus according to claim 2 wherein the transition metal is Fe.

10. An apparatus according to claim 2 wherein the stabilizing oxide is cerium oxide.

11. An apparatus according to claim 2 wherein the molecular sieve is zeolite and the stabilizing oxide is cerium oxide.

12. An apparatus according to claim 2 wherein the molecular sieve is zeolite, the transition metal includes on or more of Cu, Co, Fe, Ag and Mo, and the stabilizing oxide is cerium oxide.

13. An apparatus according to claim 2 wherein the molecular sieve is zeolite, the transition metal is Cu, and the stabilizing oxide is cerium oxide.

14. An apparatus according to claim 2 wherein the molecular sieve is zeolite, the transition metal is Fe and the stabilizing oxide is cerium oxide.

15. An apparatus according to claim 1 wherein the molecular sieve is zeolite.

16. An apparatus according to claim 15 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

17. An apparatus according to claim 15 wherein the transition metal is Cu.

18. An apparatus according to claim 15 wherein the transition metal is Fe.

19. An apparatus according to claim 15 wherein the stabilizing oxide is cerium oxide.

20. An apparatus according to claim 15 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo and the stabilizing oxide is cerium oxide.

21. An apparatus according to claim 15 wherein the transition metal is Cu and the stabilizing oxide is cerium oxide.

22. An apparatus according to claim 15 wherein the transition metal is Fe and the stabilizing oxide is cerium oxide.

23. An apparatus according to claim 1 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

24. An apparatus according to claim 23 wherein the stabilizing oxide is cerium oxide.

25. An apparatus according to claim 1 wherein the transition metal is Cu.

26. An apparatus according to claim 1 wherein the transition metal is Fe.

27. An apparatus according to claim 1 wherein the transition metal is Cu and the stabilizing oxide is cerium oxide.

28. An apparatus according to claim 1 wherein the transition metal is Fe and the stabilizing oxide is cerium oxide.

29. An apparatus according to claim 1 wherein the stabilizing oxide is cerium oxide.

30. An apparatus for removing contaminants and particulates, including nitrogen oxides and soot, from diesel engine emissions, comprising: a flow through device coated with a first catalyst comprising hematite (Fe.sub.2O.sub.3) and bixbyite ((Mn.sub.1.5,Fe.sub.0.5)O.sub.3), wherein the ratio of hematite to bixbyite ranges from 1:1 to 9:1; wherein said flow through device is in fluid communication with a reduction unit comprising a catalytic substrate coated with a second catalyst, said substrate comprising one or more transition metals supported on a molecular sieve and said second catalyst comprising one or more stabilizing oxides coating the molecular sieve.

31. An apparatus according to claim 30 wherein the molecular sieve is zeolite.

32. An apparatus according to claim 31 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

33. An apparatus according to claim 31 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo and the stabilizing oxide is cerium oxide.

34. An apparatus according to claim 31 wherein the transition metal is Cu and the stabilizing oxide is cerium oxide.

35. An apparatus according to claim 31 wherein the transition metal is Fe and the stabilizing oxide is cerium oxide.

36. An apparatus according to claim 31 wherein the stabilizing oxide is cerium oxide.

37. An apparatus according to claim 31 wherein the transition metal is Cu.

38. An apparatus according to claim 31 wherein the transition metal is Fe.

39. An apparatus according to claim 30 wherein the transition metal includes one or more of Cu, Co, Fe, Ag and Mo.

40. An apparatus according to claim 39 wherein the stabilizing oxide is cerium oxide.

41. An apparatus according to claim 30 wherein the transition metal is Cu.

42. An apparatus according to claim 30 wherein the transition metal is Fe.

43. An apparatus according to claim 41 wherein the stabilizing oxide is cerium oxide.

44. An apparatus according to claim 42 wherein the stabilizing oxide is cerium oxide.

45. An apparatus according to claim 30 wherein the stabilizing oxide is cerium oxide.