Exhaust gas purification system with an oxidation catalyst and a catalyst for selective catalytic reduction

Abstract

Exhaust gas purification system (200) coupled to an engine and comprising: an oxidation catalyst (202) with a precious metal loading of less than 75 grams (g) / cubic foot (ft3); and a selective catalytic reduction (SCR) catalyst (204) positioned downstream of the oxidation catalyst (202) and operated between 175 °C and 225 °C during engine operation to reduce the formation of N2O in the selective catalytic reduction (SCR) catalyst (204); and a reducing agent injection nozzle (210) positioned between the oxidation catalyst (202) and the SCR catalyst (204), wherein the amount of reducing agent injected between the oxidation catalyst (202) and the SCR catalyst (204) into the exhaust stream through the reducing agent injection nozzle (210) is increased while the SCR catalyst (204) is operated between 170 °C and 225 °C.

Description

[0001] The present disclosure relates to an emission control system in a vehicle with an oxidation catalyst and a selective catalytic reduction (SCR) catalyst.

[0002] Emission control devices are used in vehicles to reduce emissions, thereby reducing a vehicle's environmental impact. Catalysts, such as selective catalytic reduction (SCR) catalysts, may be used in vehicles to achieve this reduction in emissions. Additional emission control devices that can be used in vehicles include oxidation catalysts, particulate filters, three-way catalysts, etc. A diesel engine can produce a large amount of nitrous oxide (N 2 O) and other nitrogen compounds that have a particularly long lifetime in the atmosphere. Accordingly, the nitrogen compounds, such as N 2 O generated in engines are of particular environmental concern and therefore regulated for both commercial and non-commercial vehicles.

[0003] US 7,767,175 discloses an aftertreatment system with a selective catalytic reduction (SCR) catalyst positioned upstream of a diesel oxidation catalyst (DOC) wherein light-off temperatures in the system are lowered to reduce emissions. However, the inventors have recognized several disadvantages with the aftertreatment system disclosed in US 7,767,175. For example, the aftertreatment system may generate a large amount of nitrogen compounds, such as nitrous oxide, as a result of the positioning of the DOC upstream of the SCR catalyst and the interaction between the two components. In addition, the material composition of the DOC can also contribute to the increased production of nitrogen compounds such as N 2 O, contribute.

[0004] The inventors have recognized the aforementioned disadvantages of previous emission control systems and have developed an emission control system that uses an oxidation catalyst with a precious metal loading of less than 100 grams (g) / cubic foot (ft 3 ) and a Selective Catalytic Reduction (SCR) component positioned downstream of the oxidation catalyst and operated during engine operation between 150 °C and 300 °C to reduce the formation of N 2 O in the selective catalytic reduction component.

[0005] It has been unexpectedly found that maintaining the SCR catalyst within the noted temperature range and providing the noted amount of precious metal loading in the oxidation catalyst upstream of the SCR catalyst combine to reduce emissions from the emission control system. Concretely, the following reaction can take place in the SCR catalyst. 2NH 3 + 2NO 2 → N 2 O + N 2 + 3H 2 O

[0006] If the oxidation catalyst is less than 100 g / ft 3 loaded with precious metals, the amount of nitrogen oxide (NO 2 ) is reduced, thereby reducing the formation of nitrous oxide in the SCR catalytic converter. Additionally, maintaining the SCR catalyst temperature within the noted temperature range further reduces the amount of nitrous oxide formation in the SCR catalyst. In this way, emissions from the emission control system are reduced, thereby reducing the environmental impact of the vehicle. It therefore goes without saying that the technical results achieved by the aforementioned emission control system include emission reduction through the interaction between the oxidation catalyst and the SCR catalyst.

[0007] The aforementioned advantages and other advantages and features of the present specification are readily apparent from the following detailed description alone or when read in connection with the accompanying drawings.

[0008] It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It does not intend to identify key or essential features of the claimed subject matter, the scope of which is defined solely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted previously or in any part of this disclosure. In addition, the problems described above, which are acknowledged to be unknown, have been recognized by the present inventors.

[0009] figure 1 shows a schematic representation of a vehicle including an engine and an emission control system;

[0010] figure 2 illustrates an example emission control system; and

[0011] figure 3 and figure 4 illustrate a method of operating an emission control system for an engine.

[0012] An emission control system is described herein. The emissions control system includes an oxidation catalyst positioned upstream of a selective catalytic reduction (SCR) catalyst. It was unexpectedly found that the combination of a noble metal loading of the 3 oxidation catalyst that is less than 100 g / ft and the operating temperature range of the SCR catalyst, which is between 150 °C and 300 °C, achieves a drastic reduction in emissions of nitrogen compounds will. In particular, dinitrogen emissions are significantly reduced. The following reaction has been found to take place in the SCR catalyst. 2NH 3 + 2NO 2 → N 2 O + N 2 + 3H 2 O

[0013] The aforementioned noble metal loading of the oxidation catalyst reduces the amount of nitrogen dioxide that is flowed to the SCR catalyst. Therefore, according to the above equation, when the amount of nitrogen dioxide supplied to the SCR catalyst is reduced, the amount of nitrous oxide generated in the SCR catalyst is reduced. Operating the SCR catalyst within the temperature range of 150°C to 300°C further reduces the amount of nitrous oxide generated in the SCR catalyst. Consequently, the environmental impact of the vehicle is reduced. The N generated by the SCR catalytic converter 2 O can be reduced when vehicle exhaust gas temperatures are in the range of 175°C to 700°C when there is no NO 2 -Supply to the catalyst there and all the NO x is in the form of NO. If NO 2 in a concentration of up to 50% of the incoming NO x is present, the formation of N 2 O is reduced (e.g. minimized) between about 200°C and 300°C.

[0014] figure 1 is a schematic representation of a vehicle 10 with an engine 12 . The motor 12 is designed to implement combustion operation. For example, a four-stroke combustion cycle may be implemented that includes an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. However, other combustion cycles may be used in other examples. In this way, driving power in the vehicle 10 be generated. It goes without saying that the engine may be coupled to a transmission for transmitting rotational power generated in the engine to the wheels of the vehicle.

[0015] The motor 12 includes at least one cylinder 14 . However, engines with other cylinder configurations have also been considered. For example, the cylinder may be arranged in an in-line configuration with the cylinders positioned in a straight line, a horizontally opposed configuration, a V configuration, and so on.

[0016] An intake system 16 is for supplying air to the cylinder 14 designed. The intake system 16may include a variety of components to achieve the aforementioned functionality, such as a throttle, intake manifold, compressor, intake manifolds, etc. As illustrated is the intake system 16 in fluid communication with the cylinder 14 , as by an arrow 18 displayed. It goes without saying that one or more tubes, one or more channels, etc. are indicated by the arrow 18 indicated fluid communication can provide. An intake valve 20 , which is in the intake system 16 is included may provide fluid communication between the intake system and the cylinder. The inlet valve 20 can be cyclically opened and closed to implement combustion operation in the engine.

[0017] It is also a fuel delivery system 30 in the vehicle 10 intended. The fuel delivery system 30 includes a fuel tank 32 , used to store a liquid fuel 34 , such as diesel, petrol, alcohol or a combination thereof. The fuel delivery system 30 includes a fuel pump 36 in a fuel line 38 . The fuel delivery system 30 further includes a fuel injector 40 . The fuel injector 40 is shown to be directly connected to the cylinder 14 is coupled to provide a so-called direct injection of fuel. Additionally or alternatively, the fuel delivery system may include a port fuel injector for delivering fuel at a location upstream of the intake valve 20 to supply The fuel delivery system 30 may also include fuel filters, a second fuel pump, etc. In addition, the engine may further include an exhaust system 22 comprise that for receiving exhaust gas from the cylinder 14 is designed. The exhaust system may include manifolds, pipes, ducts, emission control devices (e.g., catalytic converters, filters, etc.), exhaust mufflers, etc. An exhaust valve 24 , the one with the cylinder 14 coupled is in the exhaust system 22 contain. The exhaust valve 24 may be designed to cycle open and close during combustion operation. The exhaust system 22 is in fluid communication with the cylinder 14 , as by an arrow 26 displayed. Specifically, the arrow can 26 Exhaust ports, pipes, etc. show the fluid communication between the cylinders 14 and the exhaust valve 24 provide. The exhaust valve may be configured to open and close cyclically to allow combustion operation.

[0018] The exhaust system 22 can an emission control system 50 include. The emission control system 50 may include catalytic converters, filters, temperature sensor, pressure sensors, exhaust gas composition sensor, etc. The emission control system 50 can be designed to reduce the amount of nitrogen compounds (e.g. nitrous oxide (N 2 O)) reduced in the exhaust. Consequently, vehicle emissions are reduced, thereby reducing the environmental impact of the vehicle. Specifically, the emissions control system may include an oxidation catalyst having a noble metal loading less than a predetermined level and a selective catalytic reduction (SCR) catalyst maintained within a desired temperature range. The loading of the oxidation catalyst and the operation of the SCR catalyst within a desired temperature range work together to reduce the amount of nitrogen compounds in the exhaust gas emitted from the emissions control system. An exemplary emission control system 200 is in figure 2 and discussed in more detail herein.

[0019] It can be a controller 100 be included in the vehicle. The control 100 may be configured to receive signals from sensors in the vehicle as well as command signals to components such as a reductant injector, a throttle, a valve timing adjustment system, the fuel injector 40etc. sends. Various components in the vehicle 10 can be at least partially controlled by a control system that controls 100 includes, and by input from a vehicle operator 132 via an input device 130 being controlled. In this example, the input device includes 130 an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP. The control 100 is in figure 1 as a microcomputer having a processor 102 (e.g. a microprocessor unit), input / output ports 104 , an electronic storage medium for executable programs and calibration values, which in this specific example is a read-only memory 106 (e.g., a read-only memory chip), random access memory 108 , a preservation store 110 and a data bus. The storage medium read-only memory 106 can be programmed with computer-readable data that can be processed by a processor 102 represent executable instructions for performing the methods described hereinbelow, as well as other anticipated but not specifically listed variations.

[0020] The vehicle 10 further includes a heat exchanger 70 , the one with the engine 12 is coupled. The heat exchanger 70 is designed to dissipate heat from the engine. The vehicle 10 can also have a post injector 72 comprising, with an exhaust gas flow downstream of the exhaust valve 24 is coupled. The post injector 72 is designed to add fuel to the exhaust stream at selected intervals to match the temperature components in the exhaust system. Also, an electric heater 74 in the emission control system 50 be included. The electric heater 74 is designed to add heat to one or more components of the emissions control system. The electric heater 74 may be coupled to an SCR catalyst in one example. It's also a throttle body 76 shown in the exhaust system 16 is included. The throttle 76 is designed to adjust the amount of intake airflow delivered to the cylinder.

[0021] A detailed view of an exemplary emission control system 200 is in figure 2 shown. The emission control system 200 includes an oxidation catalyst 202 . The oxidation catalyst 202 may be a diesel oxidation catalyst (DOC) in one example. The oxidation catalyst 202 may include precious metals such as palladium (Pd) and / or platinum (Pt). The amount of one or more of the aforementioned noble metals (e.g. Pd and / or Pt) in the oxidation catalyst 202 be limited to reduce the amount of nitrogen dioxide generated in the oxidation catalyst. In one example, the one or more noble metals, such as platinum (Pt) and / or palladium (Pd), can be reduced to less than 100 g / ft 3 or 75 g / ft 3 Be limited loading in the oxidation catalyst. The DOC may also include support materials such as alumina and hydrocarbon storage materials such as zeolite. The noble metals may in some cases be zoned or layered for enhanced functionality, such as a Pt-rich zone or top layer to remove hydrocarbons and carbon monoxide, followed by a Pd-rich rear zone or bottom layer to further remove residue hydrocarbons and residual carbon monoxide. Further, in one example, the oxidation catalyst need not necessarily contain platinum. Accordingly, the only precious metal in the oxidation catalyst can be palladium. This loading can limit the emission of (N 2 O) in a downstream SCR catalyst 204 reduce, which is discussed in more detail herein. As shown, the oxidation catalyst receives 202 Exhaust gas from a cylinder in an engine such as that in figure 1 shown cylinder 14 . The exhaust then passes through the oxidation catalyst202 let flow. Then the exhaust gas becomes a pipe section 206 flowed directly to the oxidation catalyst 202 is coupled. A temperature sensor 208 is with the pipe section 206 upstream of the SCR catalyst 204 and the oxidation catalyst 202 coupled. The temperature sensor 208 is configured to control the temperature of the exhaust gas in the pipe section 206 definitely. The temperature sensor 208 a temperature sensor signal can be sent to a controller, such as the in figure 1 controller shown 100 , send.

[0022] A reducing agent injector 210 is also with the pipe section 206 coupled. The reducing agent injector 210 is designed to provide a suitable reducing agent downstream of the oxidation catalyst 202 and upstream of the SCR catalyst 204 into the pipe section 206 injected. The reductant can create a desired chemical reaction in the downstream components (e.g., the SCR catalyst). The reducing agent injector 210 is in fluid communication with a reductant storage tank 212 , as by an arrow 214 displayed. One or more tubes, channels, etc. can be used to provide the aforementioned fluid communication. A suitable reducing agent 216 , such as urea (e.g. aqueous urea), ammonia (e.g. aqueous ammonia), etc., in the reducing agent storage tank 212 be in stock.

[0023] A mixer 218 is downstream of the reductant injector 210 positioned. The mixer 218 is designed to mix the exhaust gas with the reducing agent injected from the injector to improve the distribution of the reducing agent in the exhaust gas. In some cases, the mixer 218 two spirally aligned surfaces to provide this mixing.

[0024] The SCR catalytic converter 204 is downstream of the mixer 218 positioned. The SCR catalyst may include Cu or Fe containing zeolite. An exemplary zeolite may be a small pore zeolite, such as chabazite, which does not retain hydrocarbons to a high degree within its structure but allows ammonia and NOx to react at its active sites. A sensor 220 can with the SCR catalytic converter 204 be coupled. the sensor 220 can be a pressure and / or temperature sensor. the sensor 220 can be used with a controller such as the in figure 1 controller shown 100 , be in electronic communication. It was unexpectedly found that the following reaction in the SCR catalyst 204 can take place. 2NH 3 + 2NO 2 → N 2 O + N 2 + 3H 2 O

[0025] Therefore, if the amount of nitrogen dioxide supplied to the SCR catalyst is reduced by limiting the amount of noble metal loading in the oxidation catalyst to less than 100 g / ft 3 is reduced, the amount of nitrous oxide generated in the SCR catalyst is reduced, thereby reducing emissions from the emission control system. Further, in one example, the SCR catalyst may be maintained between 150°C and 300°C. Maintaining the SCR catalyst within this temperature range can further reduce nitrous oxide generation in the emission control system. The N generated by the SCR catalytic converter 2 O may be lowest at all vehicle exhaust temperatures from 175°C to 700°C when there is no NO 2 -Supply to the catalyst there and all the NO x is in the form of NO. If NO 2 in a concentration of up to 50% of the incoming NO x is present, the formation of N 2 O is reduced (e.g. minimized) between about 200°C and 300°C. Therefore, keeping the SCR catalyst between 150°C and 300°C reduces N formation 2O. Further, in some examples, the SCR catalyst may be maintained between 175°C and 225°C. Keeping the SCR catalyst within this temperature range further reduces the generation of nitrous oxide in the emission control system.

[0026] A particle filter 222 is downstream of the SCR catalytic converter 204 positioned. The particle filter 222 is designed to remove unwanted particles from the exhaust gas flowing through it. A sensor 224 can with an exhaust pipe downstream of the particulate filter 222 be coupled. the sensor 224 may be an exhaust gas composition sensor, such as a nitrogen oxide sensor, and / or a temperature sensor. the sensor 224 can be used with a controller such as the in figure 1 controller shown 100 , be in electronic communication. Accordingly, the sensor can 224 Send signals to the controller.

[0027] Components that can be adjusted to maintain a desired operating temperature of the SCR catalyst include the heat exchanger 70 , the one with the in figure 1 engine shown 12 is coupled to the in figure 1 post injection nozzle shown 72 , in the figure 1 electric heater shown 74 , in the figure 1 shown valves ( 20 and 24 ) include. If the engine is designed with variable valve timing, the throttle valve can 76 that in the exhaust system 16 is included, the in figure 1 can also be adjusted. Engine duty cycle and / or cylinder deactivation may also be adjusted to maintain a desired SCR operating temperature, where a subset of cylinders may be deactivated according to SCR temperature. Additionally, catalyst size, catalyst configuration, and / or engine power-to-weight ratio may be selected to help achieve the desired SCR catalyst operating temperature (e.g., between 175° and 225°C).

[0028] It should be understood that the one or more of the aforementioned sensors may be used to implement a feedback control strategy for temperature adjustment of the SCR catalyst. For example, a temperature indication signal from a temperature sensor coupled to the SCR catalyst or the pipe immediately upstream of the pipe may be received by a controller, and the controller may then select a component, such as the reductant injector, based on the through adjust the temperature displayed by the sensor.

[0029] figure 3 represents a procedure 300 for operating an emission control system for an engine. The method 300 can be implemented by the emission control system previously referred to figure 1 and figure 2, or it may be implemented by any other suitable emission control system.

[0030] at 302 the method includes flowing exhaust gas from a cylinder in an engine to an oxidation catalyst in an emission control system. Next, the procedure includes at 304 Flowing exhaust gas through an oxidation catalyst at less than 100 grams (g) / cubic foot (ft 3 ) Noble metal loading in the oxidation catalyst. In one example, the precious metal includes platinum. In another example, the noble metal includes palladium.

[0031] at 306 the method includes maintaining an exhaust flow through a selective catalytic reduction (SCR) catalyst between 175°C and 225°C, wherein the SCR catalyst is positioned downstream of the oxidation catalyst. at 308the method includes adjusting an amount of reductant injected into an exhaust stream between the oxidation catalyst and the SCR catalyst. It should be understood that adjusting an amount of reductant injected into the exhaust stream may include increasing the amount of reductant injected into the exhaust stream. Additionally, maintaining the SCR catalyst between 175°C and 225°C may include one or more of adjusting a heat exchanger coupled to the engine, adjusting the duty cycle of the engine, an electric heater in the emission control system, adjusting an amount of post-injected fuel in the engine, adjusting an amount of fuel injection in the engine, adjusting a throttle position in the engine, adjusting an intake valve timing in the engine, and adjusting an exhaust valve timing in the engine. The catalyst size, catalyst configuration, and / or engine power-to-weight ratio may be selected to help achieve the desired operating temperature of the SCR catalyst (e.g., between 175° and 225°C).

[0032] figure 4 provides a method 400 for operating an emission control system for an engine. The method 400 can be implemented by the emission control system previously referred to figure 1 and figure 2, or it may be implemented by any other suitable emission control system.

[0033] at 402 the method includes flowing exhaust gas through a diesel oxidation catalyst (DOC) at less than 100 grams (g) / cubic foot (ft 3 ) Precious metal loading in the DOC. Specifically, in one example, the precious metal loading of the DOC is less than 75 g / ft 3 . As also mentioned above, the precious metal may include platinum and / or palladium. In particular, in one example, the noble metal may include only palladium. Next, the procedure includes at 404 reducing the formation of nitrous oxide N 2 O in a selective catalytic reduction (SCR) catalyst by operating the SCR catalyst between 175°C and 220°C, with the SCR catalyst positioned downstream of the DOC. In one example, the formation of N is 2 O in the SCR catalyst less than 10 milligrams (mg) / mile (mi). In addition, reducing the formation of nitrous oxide N 2 O in the selective catalytic reduction (SCR) catalyst 406 include receiving a temperature indication from a temperature sensor coupled to the SCR catalyst. Reducing the formation of nitrous oxide (N 2 O) in the catalyst for selective catalytic reduction (SCR) can at 408 also one or more of adjusting a heat exchanger coupled to the engine, adjusting the duty cycle of the engine, adjusting an electric heater in the emission control system, adjusting an amount of post-injected fuel in the engine, adjusting an amount of fuel injection in the engine, adjusting a throttle position in the engine, adjusting an intake valve timing in the engine, and adjusting an exhaust valve timing in the engine based on the temperature reading.

[0034] It goes without saying that the aforementioned components can be adjusted based on the reading of the temperature sensor. In this way, the temperature of the SCR catalyst can be maintained within a desired temperature range and the DOC has a precious metal loading of less than a predetermined value to reduce the amounts of nitrogen compounds generated in the emission control system, thereby reducing emissions from the vehicle. in which the emission control system is included. Furthermore, if NO2 is not present at the SCR in the tailpipe (e.g. NO2 concentrations are below a minimum threshold), urea or ammonia can be dosed over the entire temperature range from 170 to 700 °C without forming excessive N2O. Accordingly, ammonia dosing can be adjusted not only according to temperature but also to the presence or concentration of N2O in the exhaust, with ammonia dosing being possible over a wider temperature range at lower N2O concentrations. In contrast, at higher N2O concentrations, ammonia dosing can be limited or restricted to only a smaller temperature range to reduce NO2 production.

[0035] It should be noted that the example control and estimation routines included herein can be used with various engine and / or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Accordingly, various acts, operations, and / or functions illustrated may be performed in the order illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not strictly necessary to achieve the features and advantages of the example embodiments described herein, but is provided only for ease of illustration and description. One or more of the illustrated actions, operations, and / or functions may be repeatedly performed depending on the particular strategy used. Further, the actions, operations, and / or functions described may graphically represent code to be programmed into non-transitory memory of the computer-readable storage medium in the engine control system. It should be understood that the configurations and routines described herein are exemplary in nature and that these specific embodiments are not to be construed in a limiting sense as numerous variations are possible. For example, the technology described above can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, as well as other features, functions, and / or properties described herein.

[0036] The following claims particularly set forth certain combinations and sub-combinations that are believed to be novel and non-obvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding 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 filing new claims in this or a related application. Such claims, whether broader, narrower, equal, or different, are also intended to be included within the subject matter of the present disclosure. QUOTES INCLUDED IN DESCRIPTION

[0037] This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Patent Literature Cited

[0038] US7767175 [0003, 0003]

Claims

[1] Exhaust gas purification system coupled to an engine and comprising: an oxidation catalyst with a precious metal loading of less than 100 grams (g) / cubic foot (ft³) 3 ); and a selective catalytic reduction (SCR) component positioned downstream of the oxidation catalyst and operated between 150 °C and 300 °C during engine operation to reduce the formation of N2O in the selective catalytic reduction (SCR) catalyst. [2] Exhaust gas purification device according to claim 1, wherein the precious metal comprises platinum (Pt). [3] Exhaust gas purification device according to claim 1, wherein the precious metal comprises only palladium (Pd). [4] Exhaust gas purification system according to claim 1, comprising a reducing agent injection nozzle positioned between the oxidation catalyst and the SCR catalyst. [5] Exhaust gas purification system according to claim 4, wherein the amount of reducing agent injected into the exhaust stream through the reducing agent injection nozzle is increased while the SCR catalyst is operated between 150 °C and 300 °C. [6] Exhaust gas purification system according to claim 4, wherein the reducing agent injection nozzle is in fluid communication with a reducing agent reservoir which stores ammonia. [7] Exhaust gas purification system according to claim 1, wherein the precious metal loading in the oxidation catalyst is less than 75 g / ft². 3 amounts. [8] Exhaust gas purification system according to claim 1, wherein the SCR catalyst is operated between 175 °C and 225 °C. [9] Exhaust gas purification device according to claim 1, further comprising a diesel particulate filter positioned downstream of the SCR catalyst. [10] Exhaust gas purification device according to claim 1, wherein the precious metal comprises platinum (Pt) and palladium (Pd). [11] Method for operating an exhaust gas purification system for an engine, comprising: Passing exhaust gas through an oxidation catalyst with less than 100 grams (g) / cubic foot (ft) 3 ) Precious metal loading in the oxidation catalyst; and maintaining an exhaust gas flow through a selective catalytic reduction (SCR) catalyst between 175 °C and 225 °C, with the SCR catalyst positioned downstream of the oxidation catalyst. [12] Method according to claim 11, further comprising injecting a selected amount of reducing agent into an exhaust gas stream between the oxidation catalyst and the SCR catalyst corresponding to a reduced amount of NO2 present while the exhaust gas stream is maintained between 175 °C and 225 °C through the SCR catalyst. [13] Method according to claim 11, wherein maintaining an exhaust gas flow through a selective catalytic reduction (SCR) catalyst between 175 °C and 225 °C comprises adjusting a heat exchanger coupled to the engine, adjusting the duty cycle of the engine, an electric heater in the exhaust gas purification system, adjusting an amount of post-injected fuel in the engine, adjusting an amount of fuel injection in the engine, adjusting a throttle position in the engine, adjusting an intake valve timing control in the engine, and adjusting an exhaust valve timing control in the engine. [14] Method according to claim 11, wherein the precious metal comprises platinum (Pt). [15] Method according to claim 11, wherein the precious metal comprises only palladium (Pd). [16] Method for operating an exhaust gas purification system, comprising: Passing exhaust gas through a diesel oxidation catalyst (DOC) with less than 100 grams (g) / cubic foot (ft). 3 ) Precious metal loading; and Reducing the formation of nitrous oxide N2O in a selective catalytic reduction (SCR) catalyst according to a condition by operating the SCR catalyst between 175 °C and 220 °C, wherein the SCR catalyst is positioned downstream of the DOC. [17] Method according to claim 16, wherein the formation of N2O in the SCR catalyst is less than 10 milligrams (mg) / mile (mi), and wherein the condition is an amount of ammonia stored in the SCR catalyst. [18] Method according to claim 16, wherein operating the SCR catalyst between 175 °C and 220 °C comprises adjusting a heat exchanger coupled to the engine, adjusting the duty cycle of the engine, an electric heater in the exhaust aftertreatment system, adjusting an amount of post-injected fuel in the engine, adjusting an amount of fuel injection in the engine, adjusting a throttle position in the engine, adjusting an intake valve timing control in the engine and adjusting an exhaust valve timing control in the engine. [19] Method according to claim 16, wherein operating the SCR catalyst between 175 °C and 220 °C comprises receiving a temperature reading from a temperature sensor coupled to the SCR catalyst and adjusting one or more exhaust system components based on the reading from the temperature sensor, wherein the one or more exhaust system components comprise a reducing agent injector positioned between the DOC and the SCR catalyst. [20] Method according to claim 16, wherein the precious metal loading of the DOC is less than 75 g / ft² 3 amounts.