KR20080046650A - Diesel exhaust article and catalyst compositions therefor - Google Patents

Abstract

A self-cleaning diesel exhaust particulate filter system (10) is disclosed wherein burn-off of collected particulate matter is accomplished at normal exhaust gas temperatures, the filter system being provided with a catalyst mixture of a co-formed ceria-zirconia composite and, optionally, a base metal oxide, the presence of which allows regeneration of filters at temperatures that are readily achieved in diesel exhaust systems, including operating conditions that are at low load where lower exhaust temperatures exist.

Description

Diesel exhaust gas treating apparatus and catalyst composition therefor {DIESEL EXHAUST ARTICLE AND CATALYST COMPOSITIONS THEREFOR}

Cross Reference to Related Applications

This application is priority based on US Provisional Application No. 60 / 705,823, filed August 5, 2005, entitled "Diesel Exhaust Article and Catalyst Compositions Therefor." Insist.

The present invention relates to an apparatus and catalyst composition for reducing harmful exhaust emissions from diesel engines, and more particularly to an apparatus for increasing the oxidation efficiency of particulate components in exhaust emissions.

Diesel engine exhaust gases are not only gaseous emissions such as carbon monoxide ("CO"), unburned hydrocarbons ("HC"), and nitrogen oxides ("NO _x "), but also condensate materials (liquids) that make up so-called particles or particulate matter. And solids). Total particulate matter ("TPM") emissions consist of three main components. One component is the carbonaceous fraction or the soot fraction. Such anhydrous carbonaceous material is a source of visible soot emissions typically associated with diesel exhaust.

The second component of the TPM is the soluble organic fraction ("SOF"). Soluble organic fraction is sometimes also referred to as volatile organic fraction (“VOF”), which term will be used herein. VOF can exist as a vapor or aerosol (fine droplets of liquid condensate) in diesel exhaust, depending on the temperature of the diesel exhaust, and is generally associated with the US Heavy Duty Transient Federal Test Procedure. As defined by the same standard measurement test, it is present as a condensed liquid at a standard particle collection temperature of 52 ° C. in diluted exhaust gas. These liquids include two sources: (1) lubricant swept from the cylinder wall of the engine each time the piston is raised and lowered; And (2) unburned or partially burned diesel fuel.

The third component of the particles is the so-called sulfate fraction. The sulfate fraction is formed from the small amount of sulfur present in the diesel fuel. A small amount of SO ₃ is formed during diesel combustion, which quickly combines with water in the exhaust gas to form sulfuric acid. Sulfuric acid is added to the TPM by being collected as a condensate with the particles as aerosol or adsorbed onto other particulate components.

An important aftertreatment technique currently being used to reduce particles to high levels is a diesel particle filter. There are many known filter structures that can be used to remove particles from diesel exhaust, including honeycomb wall-flow filters, winding or filled fiber filters, open cell foams, sintered metal filters, and the like. However, most attention was paid to the ceramic wall-flow filter described below. Such filters can remove more than 90% particulate matter from diesel exhaust. A filter is a physical structure for removing particles from exhaust gas. As the particles accumulate on the filter, the back pressure resulting from the filter on the engine rises. Therefore, in order to maintain an acceptable back pressure, the accumulated particles must be burned continuously or periodically from the filter. Unfortunately, carbon soot particles require temperatures of 500 to 550 ° C. or higher to burn in oxygen-rich (lean) exhaust gas conditions. This temperature is higher than the typical diesel exhaust temperature. It is generally advisable to lower the soot combustion temperature in order to provide passive regeneration of the filter. The presence of the catalyst has been found to promote the burning of soot and the regeneration of the filter at a temperature reachable in the exhaust of the diesel engine in the actual operating cycle. A catalyzed soot filter (CSF) or catalyzed diesel particle filter (CDPF) may thus be an effective way to regenerate the filter by passively burning accumulated soot while reducing the particles by more than 90%.

A common problem that occurs when using less porous CSF is caused by too fast accumulation of particulate matter on the filter, especially at lower diesel exhaust temperatures. For example, lower diesel exhaust temperatures are observed at low load conditions and at start of operation. At lower diesel exhaust temperatures, the catalyst on the filter is less effective at promoting combustion of particulate matter collected on the filter, and the back pressure in the flue gas treatment system rises. In the past, various strategies have been implemented to address the accumulation of particles on the CSF and subsequent rise in back pressure, which is described below.

For example, U. S. Patent No. 4,902, 487 discloses nitrogen dioxide produced by catalytically generated particles in the exhaust gas stream by removing the particles from the exhaust gas prior to discharge of the exhaust gas by passing the exhaust gas through the filter. Disclosed is a diesel exhaust gas treatment step of combusting with a gas containing NO ₂ ). It is also disclosed to put the catalyst upstream of the filter to achieve this. The upstream catalyst is disclosed to produce NO ₂ in a diesel exhaust stream containing nitrogen monoxide (NO).

GE 1,014,498 discloses a method and apparatus for filtering and purifying internal combustion engine exhaust gases containing solid particles. The gas is passed quickly through the first filter of a pellet type oxidation catalyst adjusted to retain larger particles, and then through a second filter surrounding the first filter, adjusted to retain smaller particles. By passing quickly toward the side, the velocity of the exhaust gas is gradually lowered. The first filter consists of pellets which are refractory and wear resistant, impregnated with an active catalyst material (eg alumina particles impregnated with cobalt oxide (Co ₂ O ₄ ) having a diameter of 1.5 to 5 mm). The second filter is made of synthetic fibers, but other materials can also be used to form the second filter.

U.S. Patent No. 4,510,265 describes a self-cleaning diesel exhaust particle filter containing a catalyst mixture of platinum group metal and silver vanadium acid, which is disclosed to lower the onset temperature of ignition and incineration of particulate matter. The filter is disclosed to include a thin film porous honeycomb (monolith) or foamed structure that allows exhaust gas to pass through a minimum pressure drop. The useful filters disclosed are made from ceramics, generally crystals, glass ceramics, glass, metals, cements, resins or organic polymers, paper, textiles and combinations thereof.

U.S. Patent 4,426,320 ("'320 patent") discloses a process for removing carbon and lead particles from internal combustion exhaust gases by passing the gas through a coarse filter followed by a fine filter. Using a relatively coarse filter in front of a fine filter allows the coarse filter to remove larger particles before the gas reaches the second fine filter and to extend the life of the fine filter. The filter is described as having a structure that slows down the rate at which the back pressure rises as particles accumulate in the filter. Catalytic material that is effective to convert one or more contaminants in the exhaust gas into harmless materials and remove suspended particles in the gas is deposited on the filter. Preferred filters are described as open cell ceramic foam filters.

Suitable catalytic materials for the combustion of carbon particles, the catalyst materials disclosed in the '320 patent include first transition series elements such as vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc. The compositions disclosed in the '320 patent are also useful in the conversion of hydrocarbon, carbon monoxide and nitric oxide contaminants. Such catalytic materials are said to have precious metals, first transition series elements and mixtures thereof.

The '320 patent contains: (1) impregnating the filter with a water soluble pyrolytic inorganic salt or complex of metal; (2) after drying the impregnated filter; (3) Direct deposition of the catalyst material on the ceramic foam support by calcining the dried filter is described. Alternatively, the catalytic material may be supported on the porous refractory inorganic oxide.

U.S. Patent No. 4,535,588 ("'588 Patent") discloses the use of a carbon particle cleaning apparatus having an embodiment in which two different filters having different air permeabilities are connected in series. A stainless steel strainer is described, wherein a filter with a higher air permeability is located upstream of a second filter with a lower air permeability. In another embodiment, ceramic or metallic foam filters having different air permeabilities are used instead of stainless steel wool filters. The filter can be coated with oxidation catalysts such as platinum, palladium and rhodium.

U.S. Patent No. 4,828,807 ("'807 Patent") discloses the use of serially connected filter elements installed in the cross section of the housing through which the exhaust gases pass, where the soot ignition temperature is reduced and the soot is burned. One or more filter elements carrying the catalyst are alternated several times with one or more filter elements carrying the catalyst to assist in the combustion of gaseous contaminants. Filter elements that can be used include sintered filter discs with open pores, discs formed from pressed ceramic fibers, in particular discs formed from fibers of Al ₂ O ₃ , SiO ₂ , aluminum silicate or ZrO ₂ ; Disks formed from sintered metal; Disks formed from the pressed bristles; And a packed layer of temperature resistant ceramic or metallic material. Numerous catalysts that assist in the ignition and combustion of particles are disclosed in the '807 patent. Such catalysts include (a) lithium oxide; (b) vanadium pentoxide; (c) a mixture of vanadium pentoxide with one or more oxides of the 37 disclosed elements, including lanthanum, cerium, praseodymium, neodymium, and zirconium; (d) vanadium salts of one or more metals listed in (c); And (e) a perenate, preferably a perenate of lithium, potassium, silver or vanadium. The catalyst is MgO, Al ₂ O ₃ , CeO ₂ , SnO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ , ThO ₂ , Nb ₂ O ₅ , WO ₃ , magnesium silicate, aluminum silicate and / or magnesium titanate and combinations thereof It is disclosed that it can be combined with a carrier material.

The '807 patent describes a catalyst that aids in the combustion of gaseous contaminants, coated on one or more filter elements comprising one or more platinum group elements, optionally in combination with one or more base metals in a temperature resistant carrier material. have. Preferred carrier materials are MgO, Al ₂ O ₃ , in particular γ-Al ₂ O ₃ , CeO ₂ , SiO ₂ , SnO ₂ , TiO ₂ , ZrO ₂ , HfO ₂ , ThO ₂ , Nb ₂ O ₅ , WO ₃ , magnesium silicate Aluminum silicate and / or magnesium titanate or combinations thereof. The carrier material is mixed with the catalyst or applied to the filter element and serves as a substrate for the catalyst.

Summary of the Invention

The present invention relates to an apparatus for increasing the oxidation efficiency of particulate components in diesel exhaust emissions. The present invention is accomplished using one or more upstream filters in communication with one or more downstream filters for the collection and subsequent combustion of particulate matter. At least one upstream filter and at least one downstream filter have a catalyst composition comprising a co-formed ceria-zirconia complex dispersed thereon.

1 shows one embodiment of the device of the present invention having an upstream soot filter and a downstream soot filter contained within a single canister.

FIG. 2 shows another embodiment of the device of the invention containing several open cell foam filters connected in series.

3 shows another embodiment of the apparatus of the present invention having a canister containing a catalyst-coated upstream open cell foam filter and a downstream catalyst-coated honeycomb wall-flow filter.

4 shows a longitudinal cross-sectional view of a wall-flow filter and gas flow through the filter.

FIG. 5 shows TGA (thermogravimetric) -DTA (differential thermal analysis) results as a function of temperature in air of catalyst test powder mixed with model SOF (lubricating oil) and model soot (carbon black).

6-10 show TGA-DTA results as a function of temperature in air of certain catalyst powders mixed with model SOF and model soot.

11-15 show TGA-DTA results as a function of temperature in helium / air as oxidizing gas of certain catalyst powders mixed with soot from model SOF and diesel engines.

16-20 show TGA-DTA results as a function of temperature in helium-NO ₂ / air as oxidizing gas of certain catalyst powders mixed with soot from model SOF and diesel engines.

21 is a plan view of a honeycomb body consisting of a perforated corrugated metal foil substrate and a perforated flat metal foil substrate having a plurality of " tabs " extending upwards on the surface of the substrate.

The apparatus of the present invention further reduces diesel particle emissions than when using only conventional wall-flow substrates. In addition, the apparatus includes a filter system that allows regeneration of the filter at temperatures readily achieved in diesel exhaust treatment systems, including operating conditions at lower loads at lower exhaust gas temperatures (ie, below 500 ° C.). To reduce the particles. Therefore, the filter in the exhaust gas treating apparatus of the present invention is much less likely to be occluded due to the accumulation of particulate matter.

The exhaust treatment apparatus has one or more upstream filters in communication with one or more downstream filters for the collection and subsequent combustion of particulate matter. Each upstream and downstream filter contains a catalyst composition that lowers the combustion temperature of the particles, which also facilitates oxidation of gaseous contaminants in the exhaust gas. The upstream filter can be an open cell foam filter characterized by low efficiency such that only a portion of the total particles in the exhaust gas are collected on the upstream filter. In another embodiment, the upstream filter can be a perforated metal foil. Soot not collected is collected in one or more filters downstream of the upstream structure. This structure is in contrast to conventional exhaust gas treatment devices which typically rely on using a single high efficiency soot filter, such as a catalyst-coated honeycomb wall-flow filter, to capture and burn particles in the exhaust stream.

1 shows an embodiment of the exhaust gas treatment apparatus of the present invention, indicated as 10, used in connection with a diesel engine. As shown, the diesel engine 12 having the engine exhaust gas outlet 14 is in fluid communication with the exhaust gas treatment apparatus 10 of the present invention. The exhaust treatment apparatus 10 includes an upstream soot filter 16 (which may be a catalyzed open cell foam filter) in fluid communication with the downstream soot filter 18. In this embodiment, a single canister 20 receives both upstream soot filter 16 and downstream soot filter 18. The canister 20 contains an inlet 22 for receiving diesel exhaust gas from the engine outlet 14 and an outlet 24 in fluid communication with the downstream filter 18.

During operation of the diesel engine 12, diesel exhaust streams containing particulate and gaseous contaminants flow out of the engine outlet 14 along the length of the exhaust gas treatment device 10. The exhaust gas stream first passes through the upstream soot filter 16, where at least some of the particles in the exhaust gas stream will be collected on the upstream soot filter 16. The exhaust gas stream then passes through the downstream soot filter 18, where further particulate matter is collected on the filter 18 and removed from the exhaust gas stream. The catalyst composition is coated on each upstream filter 16 and downstream filter 18 to promote burning of soot to regenerate each filter. The catalyst coating composition is effective in lowering the combustion temperature of the particles, in particular the soot fraction. The catalyst composition is thus useful for regeneration of the filter and lowers the back pressure in the exhaust gas treatment device due to soot collected on the filter. The composition deposited on the soot filter also converts gaseous contaminants in the exhaust gas stream into harmless gaseous products (eg carbon dioxide, water).

When using a low efficiency filter (eg open cell foam or perforated metal foil filter) as an upstream filter, the amount of particles collected on the catalyst-coated filter is increased compared to the amount of particles collected on the more efficient filter. Less. By "low efficiency" is meant that the filter removes less than 50% by weight of the particles in the exhaust stream, or typically less than 20% by weight of the particles in the exhaust stream. For example, for an open cell foam filter having a pore diameter of 0.08 inch and a web diameter of 0.01 inch, a porosity of about 5 ppi achieves this low particle collection efficiency. Since the collection of particles on the filter is reduced, a temperature lower than the temperature required in the case of thicker particle deposits on the filter can be used for combustion of accumulated particles. Using an upstream-catalyzed filter reduces the amount of particles that must be collected and burned by one or more downstream soot filters. Thus filter regeneration is achieved more easily than in the case of an exhaust treatment structure that relies on a single high efficiency catalyzed soot filter.

The upstream filter is used with one or more downstream filters. Another open cell foam or perforated metal foil filter may be used in the downstream filter or another type of filter may be used. For example, downstream filters include honeycomb wall-flow filters; Winding or filled fiber filter, sintered metal powder filter; Sintered metal fiber filter; Perforated metal foil filter; Or a ceramic fiber composite filter. Preferably, the porosity of the downstream filter is less than or equal to the porosity of the upstream open cell foam filter. The efficiency of each filter is chosen to optimize the relative trapping of the particles in each filter and to distribute the trapped particles between the filters to minimize pressure drop while maintaining good capture efficiency of the device.

In some embodiments, the exhaust treatment apparatus contains several open cell foam filters connected in series with the same porosity and the same particle filtration efficiency. For example, as shown in FIG. 2, the device 25 may contain three to five catalyst-coated foam filters. For example, FIG. 2 shows canister 30 containing three catalyst-coated open cell foam filters 32, 34, and 36 arranged in series in canister 30. The solid arrow indicates the flow direction of the exhaust gas in the canister 30 including the inlet 38 and the outlet 39. In some structures of the device 25, all three foam filters are low in efficiency (eg about 5 ppi). In other structures, the upstream filter 32 is a low efficiency filter, the first downstream filter 34 is medium efficiency (eg about 10 ppi), and the second downstream filter 36 is high efficiency (eg 20 ppi). ). As will be clear to those skilled in the art, when separate canisters are used, the filters do not need to be housed in the same canister as long as they are in fluid communication with each other.

In another embodiment, as shown in FIG. 3, the apparatus 40 contains a canister 42 containing an upstream low efficiency open cell foam filter 44 and a downstream filter 46 having a higher particle filtration efficiency. . In a preferred embodiment, downstream filter 46 is a catalyst-coated honeycomb wall-flow filter. Canister 42 contains an inlet 48 and an outlet 49 for the flow of exhaust gas through the canister. The solid arrow indicates the flow direction of the exhaust gas in the canister 42.

Sooty filter

The soot filters useful in the present invention include open cell foam filters, honeycomb wall-flow filters; Winding or filled fiber filter, sintered metal powder filter; Sintered metal fiber filter; Perforated metal foil filter; Or a ceramic fiber composite filter. Such soot filters are typically formed from refractory materials, for example ceramics or metals. In the practice of the present invention, the catalyzed filter is typically located in a canister (also referred to as a housing) that directs the fluid stream to be treated through the canister inlet to the inlet side of the filter. Soot filters useful for the purposes of the present invention include structures that allow the exhaust gas stream to pass through without significantly increasing back pressure in the apparatus or causing a pressure drop.

Open cell foam filters may be formed on refractory metallic or ceramic materials having sufficient thermal and mechanical stability for use in diesel exhaust treatment systems. Such foam filters are known in the art, and depending on the method of manufacturing the foam and the porosity, the filtration efficiency of the filter can vary. The foam filter contains a number of interconnected voids that provide an irregular path to the exhaust gas stream while the exhaust gas flows from the inlet to the outlet of the filter. Compared to the turbulence in the exhaust gas stream in the wall-flow filter, the efficiency of particle collection in the foam substrate can be increased because of the larger amount of turbulence in the exhaust gas stream generated due to this irregularity in the foam filter.

The ceramic material used to form the ceramic foam can be a refractory metal oxide, for example alumina, silica, magnesia, zirconia, titania, chromia or combinations thereof, for example cordierite or refractory metal silicates or carbides. Examples of ceramic foams are disclosed in US Pat. Nos. 4,264,347 and 6,077,060, which are incorporated herein by reference.

In one embodiment, the preferred upstream filter is a metallic open cell foam filter. Materials used to form metallic foams include steel, stainless steel, aluminum, copper, nickel, zirconium and combinations thereof. For example, numerous nickel-based foam filters are disclosed in US Pat. No. 3,111,396, which is incorporated herein by reference.

Preferred metallic open cell foam filters are formed from an alloy of iron-chromium-aluminum-yttrium (FeCrAlY), for example Porvair Fuel Cell Technology, Inc. of Hendersonville, NC. Available from. Typically, FeCrAlY filters require the application or pre-calcination step of a thermal spray containing a binder material, such as nickel-aluminate, to improve the adhesion of the catalyst washcoat to the substrate.

Open cell foam filters suitable for use as upstream filters in the exhaust gas treatment apparatus of the present invention typically contain 1 to 20 pores per inch (ppi), more preferably 1 to 10 ppi. This pore density gives the filter the ability to trap only a portion of particulate matter in the exhaust stream, thereby preventing the blockage of the upstream filter. For foam filters having a pore density of 10 to 20 ppi, the filter has a porosity of 80 to 95% (ie a theoretical density of 5 to 15%).

In another embodiment of the present invention, the upstream filter typically includes one or more metal foil sheets having a thickness of about 5 to about 100 μm. Typically, the foil consists of the same metal or metal alloy as used to make metal foil substrates of the prior art, for example titanium, stainless steel, and alloys containing iron, nickel, chromium and / or aluminum. Metallic foils may be used in one or more forms, for example it may be planar unstructured foils; Structured foils, such as foils containing wrinkles, bends, trapezoidal structures, peaks, and the like, eg, corrugated foils having creases arranged in a sinuous or "zigzag" shape; A foil having a plurality of openings, for example perforations; Foil with both pleats and multiple openings; Foils having “tabs” extending upward from the surface of the foil; It can be a foil having a combination of shapes, for example pleats, multiple openings and multiple such “tabs” and the like. In a preferred embodiment, the metal foil is a perforated metal foil, for example a PE-Kat foil filter from Emitec Corp., Urban Hills, Michigan. Metal foil filters are also described in commonly assigned co-pending US patent application Ser. No. 10 / 926,157, filed August 25, 2004, which is incorporated herein by reference.

In the case of a metal foil substrate having a plurality of openings, for the purposes of the present invention, such openings are slits, perforations, holes with a generally polygonal shape, holes with a generally oval shape and / or holes with a generally circular shape. It should be understood that it may be, or a combination of two or more of the aforementioned types of openings. Preferably, the opening comprises a hole having a generally oval or circular shape with a diameter of about 2 to about 10 mm, preferably 4 to 8 mm. Such openings will typically comprise about 10 to about 80%, preferably 20 to 60% of the foil area. This embodiment includes a flat metal foil substrate that can be perforated, with a corrugated metal foil substrate 73 having a plurality of corrugations 74 and a plurality of tabs 76 extending on the surface of the corrugated metal foil substrate ( A honeycomb body 70 containing 72 is shown in FIG. 21. Multiple perforations 78 may be contained within flat metal substrate 72 and corrugated metal foil substrate 73.

In one embodiment, the downstream filter is a honeycomb wall-flow filter. The material used to form the wall-flow filter should be relatively inert with respect to the catalyst composition dispersed thereon. The wall-flow filter and the catalyst composition deposited thereon need to be porous because the exhaust gas must pass through the walls of the carrier to exit the carrier structure.

The wall-flow filter has a number of fine, substantially parallel gas flow passages extending along the longitudinal axis of the filter body. Typically, each passageway is blocked at one end of the body and alternating passages are blocked at opposite end faces. Such monolithic carriers may contain more than about 700 flow passages (or “cells”) per square inch of cross section, but may contain fewer flow passages. For example, the carrier may have a cell ("cpsi") of about 7 to 600, more typically about 100 to 400 pieces / square inches. The cell may have a cross section that is rectangular, square, circular, oval, triangular, hexagonal, or other polygonal in shape.

4 shows a wall-flow filter 50 having a plurality of passages 52. The passage 52 is tubularly surrounded by the inner wall 54 of the filter 50. Filter 50 has an inlet end 55 and an outlet end 56. The alternating passages are blocked by the inlet plug 58 at the inlet end 55 and blocked by the outlet plug 60 at the outlet end 56, so that at the ends of the inlet 55 and the outlet 56. To form the opposite Western long substrate patterns. Gas flow 62 enters through unobstructed channel inlet 64 and flows through passage 52. Gas flow is interrupted by the outlet plug 60 and diffuses through the inner wall 54 (porous) to the outlet side 66. The gas cannot return to the inlet side of the wall because of the inlet plug 58.

Preferred wall-flow filters are ceramic-like materials such as cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, pyrite, alumina-silica-magnesia, zirconium silicate, or refractory metals such as stainless Made of steel. Preferred wall-flow filters are formed from cordierite and silicon carbide. Such materials can withstand the environment, particularly high temperatures, encountered in the treatment of exhaust gas streams.

Ceramic wall-flow filters are typically formed from materials having a porosity of about 50-60% and are typically used as downstream filters in the exhaust treatment apparatus of the present invention. For example, in some structures, cordierite wall-flow filters having a porosity of 53% and an average pore diameter of about 14 microns provide adequate exhaust gas flow. Another structure that provides less pressure drop is a wall-flow filter having a porosity of 60% and an average pore size of 26 microns.

In addition, both cell density and wall thickness affect the pressure drop and exhaust flow characteristics observed in the exhaust treatment system. Structures using a wall-flow filter having a wall of 100 cpsi and having a wall of 17 mils and a wall flow filter having a wall of 12 mils with a wall of 200 cpsi provide a flow and pressure drop across the filter useful in the device of the invention. do.

Porous wall-flow filters used in the present invention are catalyzed in that one or more catalytic materials are present on or in the walls of the elements. The catalytic material may be present at one of the inlet and outlet sides of this element wall, or at both the inlet and outlet sides, or the wall itself may be made entirely or partially of the catalytic material. The present invention includes the use of a combination of one or more catalyst material layers and one or more catalyst material layers on the inlet and / or outlet walls of the element.

Catalyst composition

The soot filter of the present invention is coated with a catalyst composition effective for the combustion of particles and gaseous contaminants (eg unburned gaseous hydrocarbons, carbon monoxide). Such catalyst compositions generally contain co-formed ceria-zirconia composites, base metal oxides, and optionally contain one or more platinum group metal components. The co-formed ceria-zirconia composite and the base metal oxide may be formed to be a single layer deposited on the substrate (to overlap each other), or the ceria composite and the base metal oxide may be used in the form of a mixture.

As used herein, the term "co-formed ceria-zirconia complex" refers to a bulk material that is a co-formed complex of ceria and zirconia, which may optionally contain other rare earth components selected from lanthanum, praseodymium, and neodymium. Co-formed ceria-zirconia complexes can be formed by techniques such as co-gelation, coprecipitation, and the like. As long as the resulting product contains ceria and zirconia dispersed throughout the particle matrix in the final product, any other technique suitable for preparing the ceria composite can be used. This technique differs from the technique of dispersing zirconia only on the surface of ceria particles or inside the surface layer only, leaving the core of a significant amount of ceria particles free of zirconia dispersion. Techniques suitable for forming co-precipitated ceria-zirconia complexes are disclosed in US Pat. Nos. 5,057,483 and 5,898,014, the manufacturing methods disclosed in these patents are incorporated herein by reference.

Cerium and zirconium salts useful for the formation of co-formed ceria-zirconia complexes are chlorides, sulfates, nitrates, acetates and the like. When the complex is formed using the coprecipitation technique, the intermediate coprecipitate can be removed after washing, spray dried or freeze dried to remove water and calcined in air at about 500 ° C. to form a co-formed ceria-zirconia complex. The co-formed ceria-zirconia composite has a surface area of at least 10 m 2 / g, preferably at least 20 m 2 / g. In co-formed ceria-zirconia complexes containing only ceria and zirconia, the proportion of ceria in the co-formed ceria-zirconia complex is generally from 20 to 95% by weight, more preferably from 40 to 80% by weight. The composition ratio of zirconia is typically 10 to 60% by weight, preferably 10 to 40% by weight of the co-formed ceria-zirconia composite.

The catalyst composition is useful for regenerating soot filters used in diesel exhaust treatment systems. The catalyst composition is soot in a diesel exhaust treatment system when the exhaust is cold, for example below 300 ° C. or typically below 200 ° C., for example when the diesel engine is operated at low loads or at the start of operation. It is useful for regenerating the filter.

The co-formed ceria-zirconia complex may optionally contain additional rare earth metal elements selected from one or more lanthanum, praseodymium and neodymium components. Rare earth metal oxides other than ceria generally form 10 to 60% by weight of the co-formed ceria-zirconia composite composition. Preferred co-formed ceria-zirconia complexes contain praseodymia in addition to ceria and zirconia. Such composites are particularly effective in lowering the combustion temperature of particles, especially soot fractions. Incorporation of such co-formed ceria-zirconia complex (containing praseodymia) is advantageous for regenerating soot filters containing deposited particles (see Examples below). Although not theoretically supported, the inventors of the present invention, praseodymia, because praseodymia is relatively easy to transfer activated oxygen to the trapped carbonaceous component comprising soot fractions, compared to other rare earth metal oxides. It is believed that it contributes to the enhanced catalytic effect of the co-formed complex. In the case of co-formed ceria-zirconia complexes containing praseodymium, generally 30 to 95 wt% ceria, 5 to 40 wt% zirconia and 10 to 60 wt% praseodymia are present in the complex. Preferably, such co-formed complexes contain 40 to 80 weight percent ceria, 5 to 25 weight percent zirconia and 20 to 40 weight percent praseodymia.

As mentioned above, preferred co-formed ceria-zirconia complexes containing praseodymia are preferably formed using techniques such as co-gelling and coprecipitation of soluble salts of a mixture of cerium with praseodymium and zirconium. It is desirable to mix all three components using the techniques described above so that all three components are evenly distributed throughout the composite matrix, wherein the co-formed ceria-zirconia complex is a solution of a soluble salt of praseodymium, for example praseodymium nitrate It is also possible, but less preferred, to load the praseodymium component by impregnation with a solution of. Impregnation of the preformed ceria-zirconia complex is disclosed in US Pat. No. 6,423,293, which is incorporated herein by reference.

The catalyst composition used to coat the soot filter in the apparatus of the present invention may contain a base metal oxide. Although not theoretically supported, it is believed that the base metal oxide makes it internally cohesive by improving the adhesion of the catalyst washcoat to the filter substrate and providing a binding action to the washcoat. The base metal oxide provides an open washcoat form that improves gas phase diffusion. In some embodiments, the base metal oxide also serves as a catalyst support for the platinum group metal component.

Preferred base metal oxides are one or more of alumina, zirconia, silica, titania, silica-alumina, magnesium oxide, hafnium oxide, lanthanum oxide and yttrium oxide. Base metal oxides are typically used in bulk form and generally have a surface area of at least 10 m 2 / g, preferably at least 20 m 2 / g. Preferred base metal oxides are alumina, preferably gamma alumina. For example, gamma alumina can have a surface area of 120 to 180 m 2 / g when used as the base metal oxide component.

Base metal oxides are generally used in amounts of 10 to 90% by weight of the catalyst composition. Preferably, the base metal oxide is incorporated into the catalyst composition at a concentration of 20 to 80 weight percent. More preferably, the catalyst composition contains a base metal oxide at a concentration of 40 to 60% by weight. For example, the catalyst composition deposited on the soot filter may contain 50% by weight of the base metal oxide with 50% by weight of the co-formed ceria-zirconia composite.

In some embodiments, it may be desirable to incorporate a washcoat binder, such as a hydrated form of alumina, such as pseudoboehmite, to improve adhesion of the catalyst composition to the filter substrate. Other binders useful in the present invention include binders formed from silica, silica-alumina and zirconia. For the purposes of the present application, such binders are considered part of the base metal oxide component of the catalyst washcoat.

In some embodiments, it may be desirable to incorporate the platinum group metal component into the catalyst composition. Useful platinum group metal components are selected from platinum, palladium and rhodium components. Incorporation of platinum group metals is useful to facilitate the combustion of gaseous components such as unburned hydrocarbons and carbon monoxide with harmless emissions. Incorporating the platinum group metal is also useful for generating nitrogen dioxide (NO ₂ ) from nitrogen monoxide (NO) to aid in the combustion of the particles. NO ₂ is known as a powerful oxidant which is particularly useful for promoting particles deposited on soot filters at lower exhaust gas temperatures than is possible using other oxidants such as molecular oxygen.

Using a solution of a water soluble salt or complex of platinum group metal (also referred to as a "platinum group metal precursor"), the platinum group metal component is onto particles of the co-formed ceria-zirconia composite, or on particles of the base metal oxide, or both By depositing on the poly, the platinum group metal component can be dispersed in the catalyst composition. Typically, an impregnation procedure is used to disperse the platinum group metal component onto the particles of the ceria composite and / or the base metal oxide component. For example, potassium chloride, ammonium thiocyanate platinum, amine-solubilized platinum hydroxide, platinum chloride, palladium nitrate and palladium chloride may be used to achieve impregnation of the co-formed ceria-zirconia complex and / or particles of the base metal oxide component. Platinum group metal precursor. When the catalyst composition is calcined, the platinum group metal precursors are converted to catalytically active metals or oxides thereof. Impregnation of the platinum group metal component on the co-formed ceria-zirconia composite and / or base metal oxide can be carried out after coating the catalyst composition onto the substrate, but impregnation is preferably carried out before coating the catalyst composition. .

In embodiments in which the platinum group metal is incorporated into the catalyst composition, generally 0.1 to 200 g / ft ³ of platinum group metal is present in the final calcined filter substrate. Since the exhaust gas treating apparatus of the present invention can be used without incorporating an upstream diesel oxidation catalyst on the flow-through substrate, the gaseous components of the exhaust gas (unburned gaseous hydrocarbons and carbon monoxide) are converted into harmless products. A platinum group metal component at a concentration sufficient for is preferably deposited on the filter substrate. In addition, as mentioned above, it is preferable to produce NO ₂ from the NO in the exhaust gas sufficient to lower the combustion temperature of the particles, especially the soot fraction. Preferably from 10 to 100 g / ft ³ , more preferably from 20 to 80 g / ft ³ of platinum group metal are present in the catalyst composition. Preferably, the platinum group metal is platinum.

If it is desired to minimize the formation of the sulfate component in the particles, lower concentrations of platinum group metal (eg 0.1 to 10 g / ft ³ ) may be used. For example, for diesel fuel containing higher levels of sulfur (not ultra low sulfur diesel fuel), it is desirable to minimize the oxidation of sulfur to SO ₃ to reduce the formation of sulfuric acid.

The upstream catalyst composition deposited on the open cell foam substrate is generally deposited at a concentration of about 0.10 to about 5.14 g / in ³ . Depending on the type of soot filter used, the downstream catalyst composition may be deposited at a concentration of 0.1 to 2.64 g / in ³ . For example, if the downstream filter is a wall-flow filter substrate, the catalyst composition is preferably deposited at a concentration of 0.25 to 0.60 g / in ³ , or 0.45 g / in ³ to 0.60 g / in ³ .

Coating of foam filter

The following is a general method of preparing a catalyst composition that can be applied to embodiments of upstream and downstream catalyst filters. In the form of an aqueous slurry of co-formed ceria-zirconia composite particles and base metal oxide particles impregnated with the co-formed ceria-zirconia composite material of the invention and the base metal oxide (eg gamma alumina), optionally with a platinum group metal component. It can be prepared as. Typically, the co-formed ceria-zirconia and base metal oxide particles are mixed with water and an acidifying agent such as acetic acid, nitric acid or sulfuric acid and ball milled to the desired particle size. This slurry is then applied to the filter substrate, dried and calcined to form a catalyst material coating (" washcoat ") thereon.

If an optional catalytic metal component is used, for example platinum, it is preferably dispersed on co-formed ceria-zirconia composite particles, or on base metal oxide particles, or on both composite particles and base metal oxide particles. . This incorporation can be carried out after the slurry containing the co-formed ceria-zirconia composite particles and the base metal oxide particles is coated as a washcoat on a suitable filter substrate. This can be done by impregnating the coated substrate with a solution of the platinum group metal precursor compound followed by drying and calcining. Preferably, however, prior to coating the slurry on the carrier, the ceria-zirconia composite particles, the base metal oxide particles, or both are impregnated with a platinum group metal precursor. In any case, the optional platinum group metal, together with a solution serving to impregnate the co-formed ceria-zirconia composite and the base metal oxide particles, is a solution of the platinum group metal precursor to the co-formed ceria-zirconia based metal oxide catalyst material. Can be added. The platinum group metal precursor is then treated chemically or via calcination to fix the platinum group metal on the particles. For example, when amine-solubilized platinum hydroxide is used as the platinum precursor, typically the amine-platinum complex is decomposed and the platinum component is adhered to co-formed ceria-zirconia and / or base metal oxide particles as poorly soluble platinum hydroxide. By adding an acid (for example acetic acid), the pH of the slurry is lowered. The particles are then dried and calcined.

Generally, a slurry of the co-formed ceria-zirconia composite and the base metal oxide particles is deposited on a filter substrate, with or without impregnation with a platinum group metal precursor solution, and then dried and calcined to adhere the catalyst material to the substrate. When the platinum group metal component is present, the platinum group metal component is converted back to the metal element or an oxide thereof. Platinum group metal precursors suitable for use in the processes described above include potassium chloride platinum, ammonium thiocyanate platinum, amine-solubilized platinum hydroxide, platinum chloride, palladium nitrate and palladium chloride, as is well known in the art.

In another catalyst composition design, separate individual layers of bulk co-formed ceria-zirconia composites, bulk based metal oxides and optionally bulk activated alumina are used. These individual layers are applied as separate coats superimposed on top of each other on the carrier. The order of applying these individual layers is not critical, and each layer (of the co-formed ceria-zirconia composite and the base metal oxide) may be first-coated or inner coat or layer, or finally-coated or outer coat or It may comprise a layer or, if present, a third coat or layer. A given layer of material can be repeated two or more times. When platinum group metal is present, it may be dispersed in any one or more individual coats or layers.

When coating the open cell foam filter of the present invention with the catalyst composition, in some embodiments, it is desirable to pretreat the foam substrate to improve the adhesion of the composition to the substrate. For example, when using FeCrAlY open cell foam substrates, the substrates are preferably subjected to the calcination step before depositing the catalyst slurry. If thicker catalyst composition washcoats are to be deposited, a metal anchor layer can be deposited on the substrate by thermal spraying the foam substrate with the chemical composition. Nickel, Ni / Al, Ni / Cr, Ni / Cr / Al / Y, Co / Cr, Co / Cr / Al / Y, Co / Ni / Cr / Al / Y, Fe / Al, Fe / Cr, Fe / Metal feedstocks selected from the group consisting of Cr / Al, Fe / Cr / Al / Y, Fe / Ni / Al, Fe / Ni / Cr, 300 stainless steel, 400 stainless steel, and mixtures of two or more thereof By arc spraying, deposition can be carried out. For the purposes of the present invention, the metal anchor layer is not considered as part of the catalyst composition. Methods for depositing metal anchor layers are disclosed in WO 99/56853, which is incorporated herein by reference.

Without depositing the anchor layer, the washcoat composition is preferably deposited on a metallic open cell foam substrate at a concentration of about 6.0 g / in ³ or less. When the anchor layer is deposited on a metallic open cell foam filter, higher concentrations, for example up to about 10 g / in ³ washcoat, may be deposited. Ceramic open cell foam filters can generally accommodate up to 15 g / in ³ .

Coating of metal foil filter

In a preferred embodiment, the coating process comprises the steps of: (a) impregnating a filter substrate in a container containing a slurry of the desired catalyst composition such that at least about 30%, preferably at least 50% of its length is impregnated; (b) centrifuging the filter substrate obtained in step (a) to distribute the coating catalyst composition on the filter substrate as a substantially uniform layer and any amount greater than the amount desired to be present on the filter substrate. Removing the coating catalyst composition; (c) drying the coated filter substrate obtained in step (c); And (d) calcining the dried coated filter substrate obtained in step (c).

Typically, step (c) will be carried out at a temperature of about 70 to about 180 ° C., preferably 80 to 120 ° C. for about 1 to about 60 minutes, preferably 15 to 30 minutes. Step (d) will typically be carried out at a temperature of about 400 to about 700 ° C., preferably 450 to 550 ° C. for about 20 minutes to about 5 hours, preferably 30 minutes to 3 hours.

If desired, the substrate is impregnated with a first slurry of coating catalyst composition such that about 30 to about 70% of its length is impregnated, and then the filter substrate is again impregnated with one or more other slurries of the other coating catalyst composition to impregnate the remaining length. Through a modified step (a), two or more different coating catalyst compositions can be coated on the filter substrate substantially uniformly.

The coating process of the present invention can be used to coat a substantially uniform filter substrate having a diameter of about 2 to about 6 inches and a length of about 1.7 to about 4 inches.

The coating process of the present invention makes it possible to provide as many substantially uniform coating layers on the filter substrate as desired. Steps (a) and (b) may be repeated as many times as desired using the same or different coating material slurry desired. Preferably, the coated filter substrate is dried after each such coating operation, and most preferably, the coated filter substrate is dried and calcined after each coating operation.

Coating of wall-flow filter

The catalyst composition may be applied to the wall-flow substrate using any means to achieve a uniform coating of the substrate. For example, an aqueous slurry containing the catalyst composition of the present invention can be applied by spray coating or brushing or dipping the surface in the slurry. Typically, after applying the catalyst slurry, air is blown through the wall-flow substrate to prevent the slurry from blocking the porous walls. Although the catalyst slurry can be dispersed on the wall-flowable substrate in the individual layers, it is desirable to disperse the catalyst composition uniformly throughout the porous wall surrounding the passageway of the substrate.

The following examples are intended to illustrate the invention and are not intended to limit the invention to the scope disclosed herein.

Model particulate matter combustion test and test results

For various catalyst powders, their ability to oxidize (burn) model particulate matter was evaluated. This evaluation was performed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) under oxidizing conditions (ie atmosphere). TGA can measure the weight loss of a material as a function of temperature and DTA can measure the heat release (heating) or heat absorption of a material as a function of temperature. In this way, the oxidation of diesel particulate matter can be measured and the oxidation performance of different catalyst compositions can be compared.

Model particulate matter was used to mimic the soot fraction and VOF of diesel particles, which have two types. One type of model diesel particulate material is a commercially available 70% by weight carbon black powder that mimics the carbonaceous soot fraction (Thermmax Powder N- of Cancarb of Medicine Hat, Alberta, Canada). A mixture of 991 (Thermax Powder N-991) and 30% lubricant (Cummins SAE-15W Premium Blue Diesel Engine Lube Oil) to mimic VOF in diesel engine exhaust. This material has been designated as the model particulate matter P1 In many diesel engines, the lubricating oil is due to the fact that VOF in diesel exhaust consists mainly of diesel lubricating oil swept from the cylinder wall and exiting through the valve guide and turbocharger seal. Is incorporated into the model particulate matter.

The second model particulate material (denoted as model particulate material P2) consists of 70% by weight of genuine soot collected from a gravimetric diesel engine and the same 30% by weight of lubricant as used in model particulate material P1. The soot fraction used in model particulate matter P2 was collected from a 98 'model 7.2 L, 300 HP engine running at 1800 RPM and 10% load. Under these conditions, the exhaust gas had a temperature of 195 ° C. For this soot collection, the engine was run on Phillips μLS fuel (3 ppm weight S).

Laboratory tests were performed using a Rheometrics (Polymer Labs) STA 1500 Simultaneous TGA / DTA device equipped with a device to incorporate oxidizing gas exposed to the sample. Three oxidizing gases were used in the evaluations described below to mimic the lean conditions and gaseous compositions encountered in diesel exhaust. The oxidizing gas was 1. flowing air (20% O ₂ ), 2. a mixture of helium and air (10% O ₂ ), 3. a mixture of air and helium and NO ₂ (5000 ppm NO ₂ and 10% O ₂ ). .

The catalyst test powders evaluated were 1. cerium oxide powder (CeO ₂ , 100% by weight), designated as test catalyst powder A; Formed ceria-zirconia composite powder 2. In the test the ball is indicated as a catalyst powder B (70 wt.% CeO ₂ - 30 wt% ZrO _2); Zirconia-ceria composite formed - 3, ball containing lanthanum oxide, denoted as catalyst powder C (55 wt% CeO ₂ - 15 wt.% ZrO ₂ - 35% by weight of La ₂ O _3); Formed ceria-zirconia composite powder 4, three plastic balls containing audio Mia, denoted as a catalyst powder D (55 wt.% CeO ₂ - 15 wt.% ZrO ₂ - 35% by weight of Pr ₆ O _11); Formed ceria-zirconia composite powder (70 wt.% CeO ₂ - 30% by weight of ZrO 5., (150 ㎡ / g with a surface area of) four platinum on a 6% by weight of gamma alumina and the ball portion, denoted as a catalyst powder E ₂ ) a catalyst composition containing 1 part; 6. It was a milled cordierite wall-flow filter base material (Corning Ex-80) as a control, indicated as Control Powder A.

Each candidate catalyst powder or control powder was mixed well with the model diesel particulate material to obtain a uniform test sample mixture containing 20% by weight model particle mixture and 80% by weight catalyst powder (or control powder). A small amount (30 mg) of test sample mixture was then placed in a sample pan of a TGA / DTA apparatus and the sample was heated at a rate of 10 ° C./min under the flow of oxidizing gas. TGA and DTA responses as a function of temperature were measured.

To illustrate the results obtained from these TGA-DTA measurements, reference is made to FIG. 5 which shows the results of the catalyst test powder mixed with the model particulate matter P1 using air as the oxidizing gas. The curve corresponding to TGA weight loss is shown as a solid curve. In the case of the catalyst illustrated in FIG. 5, weight loss and exotherm were observed in the lower temperature range (150-400 ° C.) with respect to the combustion of lubricating oil, and higher with respect to the combustion of carbon black (CB in Table 2 below). A second weight loss and exotherm was observed in the temperature range (500-800 ° C.). Each of the two individual weight losses in the TGA curve have a "start point", "inflection point" and "end point". The "inflection point" is located at the temperature associated with the highest rate of heat loss. Likewise, the exotherms in the DTA curve (indicated by dashed lines) have "start points", "peaks" and "end points", respectively. The DTA peaks correspond to the maximum heat release temperature resulting from the associated combustion process. These characteristic points in the TGA and DTA curves can be used as a figure of merit to evaluate the relative performance for different catalyst powders. For the results specified in Table 2 below, the TGA starting point and inflection temperature will be identified when it can be clearly determined for relative performance. Also, for the DTA response, the starting point and peak temperature will be used when it can be clearly distinguished from the curve.

Flowing air as oxidizing gas (20% O ₂ ) And model particulate material P1 1 rating

The catalyst powders examined in the first evaluation included Catalyst Powder A, Catalyst Powder B, Catalyst Powder C, Catalyst Powder D and Control Powder A. In Table 1 below, the compositions for the catalyst powders are summarized, and in Table 2 below the TGA-DTA results are summarized. The TGA-DTA curves obtained in each test are shown in FIGS. 6-10.

Test powder Oxide composition CeO ₂ ZrO ₂ La ₂ O ₃ Cordierite A CeO ₂ 100 B CeO ₂ -ZrO ₂ 70 30 C CeO ₂ -ZrO ₂ -La ₂ O ₃ 55 15 30 D CeO ₂ -ZrO ₂ -Pr ₆ O ₁₁ 55 15 30 Contrast Powder A Cordierite powder 100

TGA temperature (℃) DTA temperature (℃) Test powder CB start point CB Inflection Point Lube oil peak CB start point CB shoulder CB vertex A 495 591 242 440 526 599 B 494 617 227 420 530 607 C 543 631 296 466 none 621 D 476 541 309 419 none 541 Contrast Powder A 584 667 none 530 none 684

From Table 2, it can be seen that all test catalyst powders exhibit a characteristic TGA-DTA temperature for lower carbon black (CB) oxidation than Control Powder A (containing cordierite powder). Thus, the catalyst powders all showed a distinct catalytic effect. Moreover, test sample mixtures containing test catalyst powders exhibit activity against lubricating oil combustion (DTA curve), while test sample mixtures containing non-catalytic control powders do not show lubricating oil exotherm, so no oxidation has occurred. Showed In the tests performed with test sample mixtures containing the control (cordierite), the weight loss of the lubricant was essentially due to volatilization.

For tests carried out using test sample mixtures containing catalyst test powders, test catalyst powder D (containing CeO ₂ -ZrO ₂ -Pr ₆ O ₁₁ ) can be used for carbon black combustion in any of the test catalyst powders. The lowest TGA temperature response was shown (CB initiation point = 476 ° C, CB inflection point = 541 ° C). These values were 108 ° C. and 126 ° C. lower, respectively, than those obtained using cordierite controls. As a result of this comparison, the apparent catalytic effect on the test catalyst powder D was found.

The main DTA response showed that catalyst powder D and catalyst powder B (CeO ₂ -ZrO ₂ ) exhibited the lowest CB starting point temperatures of 419 ° C. and 420 ° C., respectively. This value was about 110 ° C. lower than the results obtained for the test sample mixture containing cordierite control powder. Catalyst test powder A exhibited the lowest CB peak temperature for carbon black combustion of any of the test samples evaluated (541 ° C.), while test sample mixtures containing pure ceria (catalyst powder A) were subjected to carbon black combustion at 526 ° C. Showed shoulders. The test sample mixture containing catalyst powder B exhibited the lowest DTA peak for lubricating oil oxidation (227 ° C.).

Catalyst powder C had a composition similar to catalyst powder D, except that La ₂ O ₃ was used instead of Pr ₆ O ₁₁ . The results for TGA-DTA carbon black oxidation on catalyst powder C were not as good as the results obtained using catalyst powder D. These data strongly demonstrate that Pr ₆ O ₁₁ plays an important role in the improved combustion of the soot fractions associated with catalyst powder D.

Of the catalyst powders tested, catalyst powder D was judged to have the best overall performance for lubricating oil and carbon black combustion in air. Although not theoretically supported, it is believed that the performance of the improved catalyst powder D over the catalyst powder tested is due to the presence of Pr ₆ O ₁₁ with very high lattice oxygen mobility. It is believed that an important component of the oxidation function of these metal oxide catalysts is associated with the ability of the catalyst to transfer oxygen to the particles and contribute to the oxidation of the particles.

(1) Helium / air (50:50, 10% O ₂ ), Or (2) helium-NO ₂ / Air (5000 ppm NO ₂ , 10% O ₂ Second assessment performed using oxidizing gas of) and model particulate matter P2

In this test, the model particulate material P2 provided a material that embodied more of the actual engine particles. In addition, the composition of the oxidizing gas used in the second evaluation is much more similar to the lower O ₂ concentration found in the typical diesel engine exhaust composition. In order to evaluate the effect of certain oxidants on particle oxidation, NO ₂ was added together with O ₂ . TGA-DTA tests were performed on Catalyst Powder A, Catalyst Powder B, Catalyst Powder D, Catalyst Powder E and Control Powder A. Each powder was evaluated in both helium / air and helium-NO ₂ / air.

TGA-DTA results for test sample mixtures obtained using catalyst powders can be found in Table 3 below. TGA-DTA curves for individual tests using helium / air as oxidizing gas can be found in FIGS. 11-15, while curves for tests performed using helium-NO ₂ / air are found in FIGS. 16-20. Can be.

Test powder Helium / air mixture Helium-NO ₂ / air mixture Temperature (℃) Temperature (℃) Lubricant DTA Soot DTA Soot TGA Lubricant DTA Soot DTA Soot TGA Vertex Vertex shoulder Inflection point Vertex Vertex shoulder Inflection point A 248 685 507 604 234 545 none 520 B 279 727 none 700 267 578 none 535 C 223 682 none 670 268 541 none 500 D 309 501 638 590 313 524 none 520 Contrast Powder A none 750 none 736 none 740 none 735

The results obtained using a helium-air oxidant show that the catalyst powders all oxidized soot at a lower temperature than Control Powder A (cordierite). Thus the catalytic effect on the catalyst powder is demonstrated. Of the catalyst powders tested, catalyst powder D (containing the co-formed ceria-zirconia complex containing praseodymium oxide) had the lowest temperature (501 ° C.) for the DTA soot peak and the lowest temperature (590 for the soot inflection point evaluated. ° C). Catalyst powder E containing a mixture of platinum and co-formed ceria-zirconia complex on gamma alumina exhibited the lowest lubricating oil DTA peak temperature.

The results obtained using helium-NO ₂ / air oxidant showed that for most catalyst powders, the DTA soot peak temperature and TGA soot inflection temperature were lowered by the presence of NO ₂ , known as a strong oxidant. In some cases, the difference was 140 ° C. higher than helium-air oxidant. The only exception was the result obtained from the test mixture containing catalyst powder D, in which case the presence of NO ₂ only slightly raised the DTA soot peak temperature. Nevertheless, tests performed using catalyst powder D showed the lowest DTA soot peak temperature (524 ° C.) of any candidate material tested under these conditions. When NO ₂ was present in the oxidizing gas, the DTA soot peak temperatures for the catalyst test powder were all in the range of 524 to 578 ° C. Catalyst powder E exhibited the lowest evaluated TGA soot inflection temperature (500 ° C.). The TGA soot inflection temperature was all in the range of 500 to 535 ° C. The presence of NO _{2 in} the oxidizing gas mixture did not seem to have any significant effect on the DTA or TGA soot oxidation temperature for Control Powder A (containing cordierite powder). This observation is consistent with the general effect of NO ₂ on improving the soot oxidation performance of the catalyst powder (lowering the characteristic DTA-TGA temperature).

Based on the TGA-DTA results, (containing _{CeO 2 -ZrO 2 -Pr 6 O 11} ) catalyst powder D is concluded to be a good candidate for use as part of a catalyst composition for regeneration of catalyzed diesel soot filter lost.

While the present invention has been described with a focus on preferred embodiments, it will be apparent to one skilled in the art that modifications to the preferred apparatus and methods may be used and that the present invention may be practiced otherwise than as specifically described herein. Will know. Accordingly, the invention includes all modifications that fall within the spirit and scope of the invention as defined by the following claims.

Claims (20)

An exhaust gas treatment device comprising at least one upstream filter in communication with at least one downstream filter, the upstream filter comprising an upstream co-formed ceria-zirconia composite and optionally an upstream base metal oxide. An open cell foam filter having a catalyst composition, the downstream filter comprising a downstream catalyst composition dispersed on a downstream filter, the downstream filter comprising a downstream co-formed ceria-zirconia complex and optionally a downstream base metal oxide; Is at least as porous as the downstream filter. The apparatus of claim 1, wherein the upstream and downstream co-formed ceria-zirconia composite comprises 20 to 95 wt% ceria and 5 to 80 wt% zirconia. The exhaust gas of claim 1, wherein the upstream and / or downstream co-formed ceria-zirconia composite comprises 30-95 wt% ceria, 5-50 wt% zirconia and 10-60 wt% praseodymia. Processing unit. The method of claim 1, wherein the upstream and downstream catalyst compositions contain a base metal oxide, wherein the upstream and downstream base metal oxides comprise alumina, zirconia, silica, titania, silica-alumina, magnesium oxide, hafnium oxide, lanthanum oxide and An exhaust gas treating apparatus selected from the group consisting of yttrium oxide. The system of claim 1, wherein the downstream filter comprises: a honeycomb wall-flow filter; Winding or filled fiber filters; Open cell foam filters; Sintered metal powder filter; Sintered metal fiber filter; Perforated metal foil filter; And a ceramic fiber composite filter. The apparatus of claim 4, wherein the upstream and / or downstream catalyst composition further comprises 0.01 to 200 g / ft ³ of platinum group metal component. The exhaust gas treating apparatus according to claim 1, wherein the upstream filter is more porous than the downstream filter. The exhaust gas treating apparatus according to claim 1, wherein the upstream open cell filter has a porosity of 1 to 10 ppi. The exhaust gas treatment apparatus according to claim 8, wherein the downstream filter is a honeycomb wall-flow filter. The exhaust gas treating apparatus according to claim 1, wherein the downstream filter is an open cell foam filter. The exhaust gas treating apparatus according to claim 1, wherein the downstream open cell foam filter has the same porosity as the upstream open cell foam filter. The apparatus of claim 1, wherein the downstream open cell foam filter is less porous than the upstream open cell foam filter. An exhaust gas treatment apparatus for reducing harmful exhaust emissions from a diesel engine, comprising at least one upstream filter in communication with at least one downstream filter, wherein the upstream filter or downstream filter or both are perforated metal foil filters, upstream And the filter is at least as porous as the downstream filter. The apparatus of claim 13, wherein the at least one upstream or downstream filter has a catalyst composition dispersed thereon, the catalyst composition comprising a co-formed ceria-zirconia composite and optionally an upstream base metal oxide. The apparatus of claim 14, wherein the upstream and / or downstream catalyst composition further comprises 0.01 to 200 g / ft ³ of platinum group metal component. A method of treating an exhaust gas stream exiting a diesel engine, comprising passing the exhaust gas stream through an exhaust gas treatment device comprising at least one upstream filter in communication with at least one downstream filter. An upstream catalyst composition dispersed on an upstream filter comprising a formed ceria-zirconia complex and optionally an upstream base metal oxide, the downstream filter comprising a downstream co-formed ceria-zirconia complex and optionally a downstream base metal oxide A downstream catalyst composition dispersed on a downstream filter, wherein the upstream filter is at least as porous as the downstream filter. The method of claim 16, wherein the upstream and downstream co-formed ceria-zirconia complex comprises 20-95 wt% ceria and 5-80 wt% zirconia. 17. The method of claim 16, wherein said at least one upstream and downstream filter is a perforated metal foil filter. 19. The method of claim 18, wherein the downstream filter is a honeycomb wall-flow filter. 19. The method of claim 18, wherein the downstream filter is an open cell foam filter.

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