Stratified exhaust gas treatment system, diesel oxidation catalyst system, and method for operating an engine exhaust manifold

Abstract

A stratified exhaust gas purification system (22) coupled to a vehicle engine exhaust manifold (48), comprising: a first upper layer (402) comprising a first oxidizing catalyst; a second intermediate layer (404) with an HC trap for capturing exhaust gas HCs and a third, lower layer with a second, different oxidizing catalyst, wherein the second layer (404) is positioned between the first layer (402) and the third layer, wherein the exhaust gas purification system (22) comprises a substrate support (406), wherein the substrate support (406) has a porosity that is above a threshold value, wherein the third layer is contained within the substrate support (406), and wherein the second oxidizing catalyst is configured to oxidize exhaust NOx species.

Description

FIELD OF INVENTION

[0001] The present application relates to a stratified exhaust gas purification system, a diesel oxidation catalyst system and a method for operating an engine exhaust manifold. BACKGROUND OF THE INVENTION AND SUMMARY OF THE INVENTION

[0002] In an effort to comply with strict emissions regulations, vehicle engines can be configured with an emission control system, including various emission control devices such as three-way catalysts, diesel oxidation catalysts, particulate filters, NOx catalysts, and hydrocarbon (HC) traps. The various emission control devices can be arranged in various configurations.

[0003] An example configuration is shown by Maaseidvaag et al. in US Pat. No. 6,167,696 B1. It includes a three-way catalyst upstream of an HC trap, a NOx trap, and an electrically heated catalyst. Another example configuration is shown by Yamato et al. in US Pat. No. 7,181,903 B2. It includes a three-way catalyst downstream of a NOx trap and a plasma reactor containing an HC trap. Based on the specific configuration and order of the various emission control devices in the emission control system of '696 and '903, different control strategies (e.g., temperature control strategies) are used to coordinate their activities.

[0004] However, the inventors of the present invention have identified potential problems with such systems. As one example, the different functions may compete with and / or interfere with each other. For example, NO species may be oxidized to NO2 by a diesel oxidation catalyst upstream of a NOx catalyst after an engine cold start. However, the hydrocarbon and carbon monoxide oxidation function of the diesel oxidation catalyst may interfere with the NO oxidation function of the catalyst. Consequently, even with different configurations, emissions compliance may not be achieved. This problem may worsen as emissions regulations become more stringent while combustion processes become more efficient with significantly lower exhaust temperatures.As another example, the different configurations and lower exhaust temperatures can complicate emission control device temperature control strategies. As yet another example, due to packaging volume constraints on the vehicle, the space available for the various emission control system configurations and functionalities may be limited. Overall, exhaust emissions may deteriorate.

[0005] US 7 189 376 B2, DE 10 2012 208 876 A1, DE 601 11 973 T2, DE 198 54 794 A1, DE 10 2011 119 129 A1 and DE 692 10 127 T2 disclose generic exhaust gas purification systems.

[0006] The objective technical problem to be solved can be seen as eliminating or at least reducing the disadvantages of the prior art. This problem is solved by the subject matter of the independent patent claims. In one example, some of the above problems can be at least partially addressed by a layered exhaust gas purification system coupled to a vehicle engine exhaust manifold. In one embodiment, the layered system comprises a first, upper layer with a first, oxidizing catalyst, a second intermediate layer with an HC trap for capturing exhaust HCs, and a third, lower layer with a second, different oxidizing catalyst. The second layer is positioned between the first and third layers, and all of the layers can be layered on and supported by a substrate support.In this way, different formulations can be layered onto a substrate in a selected order so that different exhaust gas purification functions can be grouped within spatial constraints to provide synergistic benefits.

[0007] For example, an emission control system may include a layered emission control device upstream of one or more NOx catalysts and particulate filters. In one example, the layered emission control device may be a layered diesel oxidation catalyst system, with multiple layers layered on and supported by a substrate support. A first, upper layer may include a first oxidizing catalyst, such as a diesel oxidation catalyst (DOC), for oxidizing exhaust hydrocarbons (HCs) and generating an exothermic reaction for downstream particulate filters or HC traps. For example, exhaust HCs may be oxidized to generate a periodic exothermic reaction, such as to assist in the regeneration of a downstream particulate filter. A second, intermediate layer may include an HC trap for capturing exhaust HCs.A third, lower layer contains a second, different oxidizing catalyst for oxidizing exhaust NO species to NO2 species. The exhaust NO2 species can then be captured or converted in a downstream NOx trap or NOx-reducing catalyst. By containing the exhaust HCs in the second layer, the NO oxidation reaction of the third layer can be protected from HC interference. In addition to a specified functionality, each layer can also have a specified washcoat loading and / or precious metal loading suitable for the specific functionality of the layer. The loadings can also be based on the vehicle application and the specific emissions profile. For example, for vehicles operating with fuels or calibrations with a higher HC content in the exhaust during a cold start, the device can be configured to increase the capacity of the second layer with the HC trap.As another example, for vehicles operating with lean-burn engines that have higher NOx levels in the exhaust, the device may be configured to increase the capacity of the third layer to enhance NO2 formation. One or more of the layers are contained within the substrate support, such as a highly porous substrate support, to reduce backpressure.

[0008] In this way, an exhaust gas purification system can be configured with different formulations in the different layers to integrate different exhaust gas purification functions and provide synergistic benefits. By reducing functional interference and enhancing functional synergy, the quality of exhaust emissions can be improved.

[0009] It should be understood that the above brief description is presented to introduce, in a simplified form, a selection of concepts that are further described in the detailed description. It is not intended to identify important or essential features of the claimed subject matter, the scope of which is defined exclusively by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that resolve any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a schematic representation of an engine system. Fig. 2 shows a schematic representation of the engine system of Fig. 1 coupled exhaust gas purification system. Fig. 3-5 show embodiments of a layered exhaust gas purification device. Fig. Figure 6 is a high-level flowchart illustrating a routine for operating the stratified exhaust gas purification device of Fig. 3-5. DETAILED DESCRIPTION

[0010] The following description relates to systems and methods for a stratified emission control device that is connected to the exhaust manifold of an engine system, such as the engine system of Fig. 1. The stratified exhaust gas purification device may be a stratified diesel oxidation catalyst (DOC) system, as described in Fig. 2, positioned in front of one or more other emission control devices, such as one or more NOx-reducing catalysts and particulate matter (PM) filters coupled to the engine exhaust manifold. The various layers of the layered device may contain different formulations to enable the performance of different emission control functions within the spatial constraints of the device. The various formulations may be layered, as shown in Fig. 3-5 to reduce functional disruption while enabling functional synergies. As shown in Fig. As shown in Figure 6, exhaust gas can be passed over and through the stratified device to trap and oxidize exhaust hydrocarbons and raise the exhaust temperature, while exhaust NO species are oxidized to NO2 for subsequent capture on a downstream NOx trap or low-temperature reduction in a closed-loop selective catalytic reduction (SCR) catalyst using urea or another NOx reductant. In this way, the quality of exhaust emissions can be improved.

[0011] Fig. 1 shows a schematic representation of an engine system 8 having an engine 10 with a plurality of cylinders 30. The engine 10 includes an engine intake 23 and an engine exhaust 25. The engine intake 23 includes a throttle valve 62 fluidly coupled to the engine intake manifold 44 via an intake passage 42. The engine exhaust 25 includes an exhaust manifold 48 leading to an exhaust passage 35 that directs exhaust gas to the atmosphere. The engine exhaust 25 includes an emission control system 22 having one or more emission control devices 70 mounted in a closely coupled position. The one or more emission control devices may have various combinations and arrangements (as in Fig. 2 shown) of one (in Fig. 3-5), a three-way catalyst, a lean NOx trap, a closed-loop catalyst, a diesel particulate filter, an oxidation catalyst, etc. It is understood that other components may be included in the engine, such as a variety of valves and sensors.

[0012] In some embodiments, the engine intake 23 may further include a boosting device, such as a compressor 74. The compressor 74 may be configured to draw in intake air at atmospheric pressure and boost it to a higher pressure. The boosting device may be a compressor of a turbocharger, with the boosted air introduced upstream of the throttle valve, or the compressor of a supercharger, with the throttle valve positioned upstream of the boosting device. Using the boosted intake air, boosted engine operation may be performed.

[0013] The engine system 8 may be coupled to a fuel system 18 that includes a fuel tank 20 coupled to a fuel pumping system 21. The fuel tank 20 may contain multiple fuel blends, including a fuel having a range of alcohol concentrations, such as various gasoline-ethanol blends including E10, E85, gasoline, etc., and combinations thereof. The fuel pumping system 21 may include one or more pumps for pressurizing fuel supplied from the fuel injectors of the engine 10, such as the exemplary injector 66. Although only a single injector 66 is shown, additional injectors are provided for each cylinder. It should be understood that the fuel system 18 may be a recirculating fuel system, a recirculating fuel system, or various other types of fuel systems.

[0014] The vehicle system 6 may further include a control system 14. The control system 14 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81 (various examples of which are described herein). As one example, the sensors 16 may include an exhaust gas sensor 126 located upstream of the emission control device, a temperature sensor 128, and a pressure sensor 129. Other sensors, such as additional pressure, temperature, air-fuel ratio, and composition sensors, may be coupled to various locations in the vehicle system, as discussed in more detail herein. As another example, the actuators may include a fuel injector 66 and a throttle valve 62. The control system 14 may include a controller 12.The controller can receive input data from the various sensors, process the input data, and trigger the actuators in response to the processed input data based on an instruction or code programmed therein corresponding to one or more routines. An example control routine is described here with respect to . Fig. 6 described.

[0015] Fig. 2 shows an embodiment of the emission control system 22. The emission control system 22 may include one or more emission control devices coupled to an engine exhaust manifold. These may include, for example, a stratified diesel oxidation catalyst device (or stratified diesel oxidation catalyst system) 202 positioned upstream of a NOx control device 204 and a PM control device 206. The NOx control device may include, for example, a lean NOx trap (LNT) or a NOx-reducing catalyst (e.g., a closed-loop catalyst), while the PM control device may include, for example, a PM filter or a diesel particulate filter (DPF). While the embodiment shown shows the NOx control device 204 upstream of the PM control device 206, in alternative embodiments, the NOx control device 204 may be positioned downstream of the PM control device 206.By positioning the stratified DOC device 202 upstream of the NOx control device and the PM control device, various benefits can be achieved. For example, exhaust hydrocarbons in one of the layers of the stratified DOC device can be oxidized to raise the temperature of the exhaust gas above a threshold temperature, such as above a regeneration temperature of the PM device. As another example, exhaust hydrocarbons in one of the layers of the stratified DOC device can be retained to reduce functional interference of the hydrocarbons with the NOx control device. In this way, by passing exhaust gas over (and through) the stratified DOC device before passing the exhaust gas over the downstream NOx catalysts and PM traps, various exhaust components can be progressively processed and the quality of the exhaust emissions can be improved.

[0016] Although not shown, a reductant delivery system may be included in the exhaust gas purification system 22, for example, upstream of the NOx control device. The reductant delivery system may be configured to inject an appropriate reductant (such as ammonia or urea) into the exhaust gas immediately before the exhaust gas enters the NOx control device.

[0017] Various embodiments of the layered diesel oxidation catalyst device (202) of Fig. 2 are here at Fig. 3-5. The various embodiments include embodiments in which multiple layers with proprietary formulations are layered on and supported by a substrate support, as well as embodiments in which one or more formulations are included in the same layer and one or more layers are layered within the substrate support.

[0018] With reference to Fig. 3, a first embodiment 300 of a stratified exhaust gas purification system (such as the stratified diesel oxidation catalyst system of Fig. 2) which is connected to a vehicle engine exhaust manifold (such as the exhaust manifold of Fig. 1). The layered system includes a first, upper (or outer) layer 302 containing a first oxidizing catalyst. The first oxidizing catalyst may be, for example, a diesel oxidation start catalyst. The layered system further includes a second intermediate layer 304 with an HC trap for capturing exhaust HCs. The layered system also includes a third, lower (or inner) layer 306 with a second, different oxidizing catalyst. The second oxidizing catalyst is a NO oxidation catalyst configured to oxidize exhaust NO species to NO2 species. The second layer 304 is positioned between the first and third layers 302, 304. The layered system further comprises a substrate support 308. In particular, the second layer 304 may be layered on top of the third layer, and the first layer 302 may be layered on top of the second layer.The substrate support 304 may be made of any suitable material, such as cordierite, aluminum titanate, mullite, or silicon carbide. Furthermore, the substrate support may have a porosity of 42 to 65%. In yet further embodiments, the substrate support may include a diesel particulate filter (DPF) with multiple channels with blocked alternating ends. As such, various suitable particulate filters may be used, including cordierite, aluminum titanate, mullite, and silicon carbide.

[0019] The first oxidizing catalyst of the first layer 302 may be configured to oxidize exhaust HCs to raise an exhaust temperature above a threshold temperature. For example, the first oxidizing catalyst of the first layer may oxidize exhaust HCs to periodically generate an exothermic reaction for downstream particulate filters or HC traps. In this way, exhaust heat may be maintained above a threshold required for the improved functioning of downstream emission control devices, such as for the regeneration of a downstream particulate matter filter. Incorporating the HC-oxidizing catalyst into one of the layers may also reduce the need for a dedicated start-up catalyst or other exhaust heat-maintaining device.

[0020] The second oxidizing catalyst of the third layer 306 may be configured to trap exhaust NOx species. For example, the second layer may have microporosity configured to retain exhaust HC species within the second layer 304 and prevent the HCs from penetrating the third layer 306. The second layer may be sized to allow the passage of exhaust NOx species through the second layer into the third layer. In this way, the second layer containing the HC trap may act as a molecular sieve, filtering out high molecular weight HCs during lean-burn or low-temperature conditions and protecting the third-layer NOx oxidizing catalyst from the detrimental thermal effects of HC adsorption.By integrating the NOx oxidizing catalyst into one of the layers, the need for a dedicated NOx oxidation device, such as a plasma reactor, can be reduced. Furthermore, the third layer can be configured to capture NOx species during engine cold starts and thermally desorb the NOx species at normal operating temperatures of the emission control device.

[0021] In the embodiment shown, only the diesel oxidation start catalyst can be included in the first layer, while the HC trap and the NO oxidizing catalyst are excluded from the first layer. Similarly, only the HC trap can be included in the second layer, while the first and second oxidizing catalysts are excluded from the second layer, and only the NO oxidizing catalyst can be included in the third layer, while the HC trap and the diesel oxidation catalyst are excluded from the third layer. In this way, the different functionalities can be confined to different layers to reduce functional interference while enabling synergy between the functions.

[0022] The different layers can be configured with different washcoat loadings. Furthermore, the precious metal loading of the different layers can vary. For example, the first layer can have a first washcoat loading and a first precious metal loading, the second layer can have a second washcoat loading and a second precious metal load, and the third layer can have a third washcoat load and a third precious metal load. The first, second, and third washcoat loading and the precious metal loadings can be selected based on the functionality of the layer. For example, some layers (e.g., the first DOC layer) may contain a higher precious metal loading, while other layers (e.g., the third NO oxidizing layer) may not contain any precious metals. Furthermore, the loadings can be tailored to a specific vehicle application and a specific engine exhaust emission profile.In still other embodiments, the washcoat and precious metal loadings can be adjusted based on the engine-off HC content. In one example, the total washcoat loading can be in the range of 1.25 to 4.5 g / in. 3 with different washcoat charge distributions for the different layers.

[0023] As an example, the washcoat loading of the first layer 302 including the diesel oxidation catalyst may be 0.25 to 1.5 g / in 3 The first layer 302 may also contain a precious metal charge with a platinum (Pt) and palladium (Pd) content of 2 to 180 g / ft 3 The Pt to Pd ratio can range from 2:1 to 0:1. In one example, the Pt-Pd ratio can be 1:4.

[0024] The washcoat loading of the second layer 304 including the HC trap can be 0.5 to 1.5 g / in 3The second layer 304 may further comprise zeolite material of a corresponding family with aluminosilicates and silicoaluminophosphates (SAPOs). That is, in the embodiment of Fig. 3, the first and third layers may not contain any zeolite material. The zeolite material of the second layer 304 may further contain ion-exchanged metals such as Ag, Au, Cu, Fe, and / or other metals known to promote HC adsorption. The washcoat loading of the third layer 306, including the NO oxidation catalyst, may be 0.5 to 1.5 g / in 3The third layer 306 may be configured not to contain any Pt group metals. Rather, the third layer may contain mixed metal oxides. In particular, the third layer may contain a single metal oxide or mixtures in a range of 2 to 20 wt. % in the layer. In one example, the mixed metal oxides may primarily contain Mn or Co. In another example, the mixed metal oxides may secondarily contain W and Mo or tertiarily contain Cu and Fe.

[0025] Fig. 4 shows an alternative embodiment 400. Here, the layered diesel oxidation catalyst (DOC) system includes a first DOC layer 402 configured to oxidize exhaust hydrocarbons to raise an exhaust gas temperature, and a second DOC layer 404 configured to trap exhaust hydrocarbons and prevent them from entering the substrate support. In the embodiment shown, the DOC system includes a substrate support 406 having a higher porosity (e.g., above a threshold). The highly porous substrate support may have a porosity of 40 to 80%. The highly porous grade of substrate support 406 may, for example, include highly porous cordierite or silicon carbide as in the highly porous substrate support of the previous embodiments. Still further, the highly porous substrate may include a highly porous DPF substrate having a porosity in the range of 40 to 80%.

[0026] The use of such a highly porous substrate support enables the integration of an additional catalyst or formulation into the substrate support. As shown, a third layer with the second, NO oxidizing catalyst is contained in the substrate support 406, while the first and second DOC layers 402, 404 are carried by the substrate support 406. By integrating at least one of the layers into the substrate support, further compaction is achieved within spatial constraints, while also reducing the exhaust backpressure occurring in the layered exhaust gas purification device. In addition, the achievement of a light-off temperature can be accelerated. The washcoat loading of the various layers as well as the precious metal content of the various layers of the embodiment of Fig. 4 can be similar to those previously with reference to the embodiment of Fig. 3 described.

[0027] Fig. 5 shows yet another embodiment 500. Here, the layered diesel oxidation catalyst (DOC) system includes a first DOC layer 502 configured to capture and oxidize exhaust gas hydrocarbons. That is, the first and second layers of the embodiments of Fig. 3-4 are combined or contained within each other to provide synergistic benefits. In this first combined layer, exhaust HC may be trapped, and the trapped exhaust HCs may be oxidized by the first oxidation catalyst to raise exhaust temperature and periodically generate an exothermic reaction for downstream emission control devices. The layered system may further include a second DOC layer 504 comprising a substrate support (e.g., a highly porous substrate support) in which the second NOx-oxidizing catalyst is layered, as previously described in Fig. 4. In other words, the second layer is contained in the substrate carrier. Therefore, in the embodiment of Fig. 5 only the first layer may contain zeolite and Pt group metals (i.e., the second layer may not contain zeolite or Pt group metals), while only the second layer may contain mixed metal oxides (i.e., the first layer may not contain mixed metal oxides).

[0028] With reference to the embodiment of Fig. 5, the total washcoat load can be in the range of 1.25 to 4.5 g / in 3 remain, with the specifications of the starting catalyst, the HC trap and the NO oxidation catalyst remaining the same as previously Fig. 3. However, the washcoat charge distribution between the layers may vary. In one example, the washcoat charge of the first combined layer with the first HC oxidation catalyst function and the HC trap function may be 0.75 to 2.5 g / in 3 while the washcoat loading of the second layer with the substrate support and the NO oxidation catalyst is 0.5 to 2 g / in 3 can amount to.

[0029] In each of the embodiments of Fig. 4-5, the first DOC or layer is configured to charge a first amount of exhaust hydrocarbons, while the second DOC or layer is configured to charge and oxidize a second amount of exhaust NOx species and potentially capture NOx during a cold start. In one example, the second amount of charge may be greater than the first amount of charge. In an alternative example, the second amount may be less than the first amount of charge. The layers may also differ in their qualitative composition. For example, the first DOC layer may contain precious metals such as platinum and / or palladium, while the second DOC layer may contain a base metal such as manganese without such precious metals.

[0030] It is understood that while the embodiments of Fig. 3-5 show the different formulations as different layers stacked on a substrate support. In alternative embodiments, the different formulations can be contained in separate substrates or bricks. As such, layering the different functionalities can better meet spatial constraints without compromising functional efficiency.

[0031] Now with reference to Fig.6, an exemplary method 600 of operating an upstream stratified emission control device and one or more other downstream emission control devices coupled to an engine exhaust manifold is shown. By passing exhaust through the stratified emission control device before passing the exhaust through the other emission control devices, additional exhaust processing can be achieved within the spatial constraints of the exhaust manifold while also reducing functional interference.

[0032] At 602, the routine includes passing exhaust gas over a substrate of the stratified device (such as the stratified DOC system) and through a plurality of catalytic layers supported by the substrate. At 604, the routine includes oxidizing exhaust hydrocarbons in a first upstream catalytic layer of the device. Here, by oxidizing exhaust hydrocarbons in the first layer, a temperature of the exhaust gas may be raised above a threshold temperature, such as a PM filter regeneration temperature. That is, a periodic exothermic reaction may be created for retaining heat in the exhaust system, thereby improving the performance of downstream emission control devices.

[0033] At 606, the routine includes retaining exhaust hydrocarbons in a second intermediate catalytic layer of the device. By retaining the exhaust HCs in the second layer, the catalytic activity of the third, lower layer may be protected from HC interference. At 608, the routine includes oxidizing exhaust NO species in a third downstream catalytic layer of the device. In particular, exhaust NO may be oxidized to NO2 for subsequent capture and processing in a downstream NOx trap or continuous reduction by a controlled catalyst. As such, in embodiments of the device where the substrate is of a higher porosity grade and the third layer NO-oxidizing catalyst is contained within the substrate, oxidizing exhaust NO species in the third layer includes oxidizing exhaust NO species within the substrate support.After passing the exhaust gas over the substrate and multiple layers of the layered device, the routine at 610 may include passing the exhaust gas through one or more of a NOx trap or a controlled catalyst and a PM filter positioned behind the substrate in the exhaust manifold.

[0034] In this way, different emission control functions and formulations can be layered onto a substrate carrier to integrate the various emission control functions within the packaging volume constraints of a vehicle engine exhaust manifold. By organizing the configuration of the layers to enhance synergistic benefits while reducing functional interference, the quality of exhaust emissions can be improved.

[0035] It should be understood that the configurations and process flows disclosed herein are exemplary in nature and that these specific embodiments are not to be considered in a limiting sense, as numerous variations are possible.

[0036] The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations and other features, functions, and / or properties disclosed herein. The following claims particularly point out certain combinations and sub-combinations that are considered novel and non-obvious. These claims may refer to "a" element or "a first" element, or the equivalent thereof. Such claims should be understood to include the incorporation of one or more such elements, neither requiring nor precluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed by amending the present claims or by presenting new claims in this or a related application.Such claims, whether broader, narrower, equal, or different in scope to the original claims, are also deemed to be included within the subject matter of the present disclosure. Reference symbol lists for FIG. 6 602 Sending exhaust gas over a substrate from and through the multiple layers of the layered DOC system 604 Oxidation of exhaust gas HCs in a first upstream catalytic layer and raising the exhaust gas temperature 606 Retention of exhaust gas HCs in a second catalytic intermediate layer 608 Oxidation of exhaust gas NO in a third downstream catalytic layer 610 Sending exhaust gas through the NOx trap and / or PM filter, positioned behind the coated DOC system in the exhaust manifold End - End

Claims

[1] A stratified exhaust gas purification system (22) coupled to a vehicle engine exhaust manifold (48), comprising: a first upper layer (402) comprising a first oxidizing catalyst; a second intermediate layer (404) with an HC trap for capturing exhaust gas HCs and a third, lower layer with a second, different oxidizing catalyst, wherein the second layer (404) is positioned between the first layer (402) and the third layer, wherein the exhaust gas purification system (22) comprises a substrate support (406), wherein the substrate support (406) has a porosity that is above a threshold value, wherein the third layer is contained within the substrate support (406), and wherein the second oxidizing catalyst is configured to oxidize exhaust NOx species. [2] The exhaust gas purification system (22) of claim 1, wherein the first oxidizing catalyst is configured to oxidize exhaust HCs to raise an exhaust gas temperature above a threshold temperature. [3] The exhaust gas purification system (22) of claim 1, wherein the second oxidizing catalyst is configured to capture exhaust NOx species. [4] The exhaust gas purification system (22) of claim 1, wherein the second layer (404) has a porosity configured to retain exhaust HC species in the second layer (404) and allow exhaust NOx species to pass through the second layer (404) into the third layer. [5] The exhaust gas purification system (22) of claim 1, wherein only the second layer (404) contains a zeolite. [6] The exhaust gas purification system (22) of claim 1, wherein one or more of the first, second and third layers (402, 404) further comprise a diesel oxidation catalyst. [7] The exhaust gas purification system (22) of claim 1, wherein the first layer (402) has a first washcoat loading and precious metal content, the second layer (404) has a second washcoat loading and precious metal content, and the third layer has a third washcoat loading and precious metal content, wherein the first loading is different from each of the second and third loadings, and wherein the first content is different from each of the second and third contents. [8] A layered diesel oxidation catalyst system (400) comprising: a first DOC layer (402) configured to capture exhaust hydrocarbons and / or oxidize exhaust hydrocarbons to raise an exhaust gas temperature; a second DOC layer (404) configured to capture exhaust NOx species and / or oxidize exhaust NO, and a third, lower layer with a second, different oxidizing catalyst, wherein the second layer (404) is positioned between the first layer (402) and the third layer, wherein the diesel oxidation catalyst system (400) comprises a substrate support (406), wherein the substrate support (406) has a porosity above a threshold value, wherein the third layer is contained within the substrate support (406), and wherein the second oxidizing catalyst is configured to oxidize exhaust NOx species. [9] The diesel oxidation catalyst system (400) of claim 8, wherein the first and second DOC layers (402, 404) are supported by the substrate support (406). [10] The diesel oxidation catalyst system (400) of claim 9, wherein the second layer (404) is contained in the substrate support (406). [11] The diesel oxidation catalyst system (400) of claim 8, wherein the first layer (402) contains zeolite and the second layer (404) does not contain zeolite. [12] The diesel oxidation catalyst system (400) of claim 8, wherein each of the first and second layers (402, 404) contains a diesel oxidation catalyst. [13] The diesel oxidation catalyst system (400) of claim 8, wherein the first layer (402) contains Pt and / or Pd and wherein the second layer (404) does not contain Pt or Pd. [14] A method (600) for operating an exhaust gas purification system (22) coupled to an engine exhaust manifold (48), comprising: Sending exhaust gas over a substrate of the exhaust gas purification system (22) and through a plurality of catalytic layers (402, 404) supported by the substrate; Oxidation of exhaust gas hydrocarbons in a first upstream catalytic layer (402) of the exhaust gas purification system (22); Retaining exhaust gas hydrocarbons in a second catalytic intermediate layer (404) of the exhaust gas purification system (22) and Oxidation of exhaust gas NO species in a third, downstream catalytic layer of the exhaust gas purification system (22), wherein the diesel oxidation catalyst system (400) comprises a substrate support (406), wherein the substrate support (406) has a porosity that is above a threshold value, wherein the third layer is contained within the substrate support (406), and wherein oxidizing exhaust NOx species in the third layer includes oxidizing exhaust NO species in the substrate support (406). [15] The method (600) of claim 14, further comprising, after passing the exhaust gas over the substrate of the emission control system (22), passing the exhaust gas through a NOx trap, a NOx reducing catalyst and / or a PM filter positioned behind the substrate in the engine exhaust manifold (48). [16] The method (600) of claim 15, wherein oxidizing exhaust hydrocarbons in the first layer (402) includes raising a temperature of the exhaust gas above a regeneration temperature of the PM filter.

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